Biomedical subjects

M Rendell

Publications and source records attributed to M Rendell.

At least 19 recordsLinked to original sources

PubMed1992

Red cell filterability determined using the cell transit time analyzer (CTTA): effects of ATP depletion and changes in calcium concentration.

Cell transit time analysis (CTTA) is a new filtrometric technique for assessing red blood cell deformability by measuring the conductivity change caused by passage of erythrocytes through a polycarbonate filter. Most reported studies to date using CTTA have focused on the transit time (TT), the duration of passage of an individual red cell through a micropore. Bulk flow rate has not been previously measured via CTTA. The use of new enzyme based cleaning solutions make it possible to reduce clogging in micropore filters. Therefore, valid measures of the number of red cell transits per unit time (counts/s: C/S) can now be obtained. We evaluated both parameters, TT and C/S, as indicators of red cell filterability. Our goal was to evaluate the effect of metabolic changes shown by alternative techniques to affect red cell deformability. The two best established factors are changes in intracellular [ATP] and [Ca2+]. ATP depletion produces a very small increase in TT but a very marked decrease in C/S. In contrast, the addition of low concentrations of calcium produces an increase in TT with minimal decrease in C/S. The effects of calcium appear to be complex. The substantial changes in intracellular calcium induced by the ionophore A23187 result in a curvilinear pattern of increase in transit times and reduction in counts per s. Lanthanum, which inhibits egress of intracellular calcium, causes an increase in TT with a drop in C/S. We conclude that CTTA demonstrates the same changes in red cell deformability measurable by alternative filtrometric techniques; however, CTTA furnishes two separate and independent parameters which may be used to evaluate red cell deformability.

Adenosine Triphosphate↗

PubMed1992

Diabetic cutaneous microangiopathy.

PURPOSE: To determine a potential relationship between skin blood flow changes and the duration of diabetes and the presence of other microvascular complications. PATIENTS AND METHODS: Skin blood flow was measured by laser Doppler techniques at the finger and toe pulps, areas of predominant arteriovenous anastomotic (AVA) flow, and on the finger and toe dorsums, which have a greater nutritive microvascular contribution, in 83 diabetic patients and 39 nondiabetic control subjects. The average duration of diabetes was 14 +/- 1 years. Thirty-four patients had retinopathy. Eighteen patients had proteinuria. Forty patients had definite signs and symptoms of neuropathy, whereas 11 had no detectable neuropathy. RESULTS: There was little difference between diabetic and nondiabetic skin blood flow at normal body temperatures. However, at an elevated skin temperature of 44 degrees C, significant reductions in skin blood flow versus control were demonstrated in the diabetic group. Skin blood flow at finger and toe dorsums showed a decrease as a function of the duration of diabetes. In contrast, there was little, if any, relationship between the duration of diabetes and skin blood flow at the finger and toe pulps. Diabetic patients with retinopathy had significantly lower blood flow at both finger and toe dorsums than those without retinopathy. Even excluding patients with recent onset of diabetes from the analysis, flows at finger (18.6 +/- 2.0 mL/min/100 g) and toe dorsums (11.2 +/- 1.4 mL/min/100 g) in the patients with retinopathy were significantly lower than in diabetic patients without retinopathy [finger: 28.6 +/- 2.7 mL/min/100 g (p < 0.01) and toe: 15.1 +/- 1.5 mL/min/100 g (p < 0.05)]. The presence of proteinuria was also associated with lower blood flow at the toe dorsum. There were no differences between patients with or without clinical diabetic neuropathy. At finger and toe pulps, there were no significant differences between diabetic patients with or without retinopathy, proteinuria, or neuropathy. CONCLUSIONS: There appears to be a diabetic cutaneous microangiopathy that coexists with diabetic retinal and renal microvascular disease. This process is expressed primarily at sites of nutritive microvasculature. The ability to use the skin as a model for diabetic microangiopathy would have great practical importance, both experimentally and in clinical practice.

Adult↗

PubMed1992

Skin blood flow and current perception in pentoxifylline-treated diabetic neuropathy.

There are several anecdotal reports of improvement in diabetic sensory neuropathy following a course of pentoxifylline therapy. Pentoxifylline theoretically could improve skin blood flow, thus reducing ischemia at axonal endings. The authors used laser Doppler techniques to measure skin blood flow and measured sine wave current perception thresholds (CPTs) in pentoxifylline-treated diabetic patients with sensory neuropathy. Twenty-four patients completed a six-month course of treatment. These patients had a predominantly "stocking" neuropathy; all the major abnormalities on clinical, laser Doppler, and current perception testing were found on the lower extremity. Seventeen of the 24 patients reported symptomatic improvement. A careful, graded neurologic examination confirmed that improvement, with a decrease in symptom score on the lower extremity (SSDW) from a baseline of 5.0 +/- 0.7 to 3.5 +/- 0.7 (p < 0.01) and of physical score (PSDW) from baseline 22.0 +/- 2.0 to 16.0 +/- 1.9 (p < 0.01) after six months. On the lower extremity, there was an increase in laser Doppler measured flow score (FS) both at 35 degrees and at 44 degrees C. FSDW (35 degrees) increased from 10 +/- 2 to 14 +/- 3 at six months (p < 0.05). FSDW (44 degrees) increased from 58 +/- 5 to 77 +/- 7 at six months (p < 0.01). There was an improvement in sine wave current perception measured by current perception threshold score (TS). TSDW dropped from 150 +/- 32 to 84 +/- 28 at six months (p < 0.03). In patients with diabetic sensory neuropathy, pentoxifylline appears to improve skin blood flow. Current perception thresholds improve in tandem, corroborating improvement in clinical neurologic findings.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1991

Effects of glycemic control on red cell deformability determined by using the cell transit time analyzer.

There is considerable evidence that blood viscosity is greater than normal in diabetes, and decreased red blood cell deformability has been suggested as the cause. However, viscosity can be influenced by changes in the properties of blood proteins in addition to red cells. Direct interpretation of red cell filtrometry data in terms of deformability has been complicated by the interfering effect of white cells and platelets and clogging of micropores. We have thus used the cell transit time analyzer, a new filtrometric procedure that eliminates these complications and produces an individual red cell micropore transit time profile, to reassess diabetic red cell deformability. Samples from 26 patients with diabetes and an equal number of subjects without diabetes who served as controls were assayed by the cell transit time analyzer at 2 and at 4 cm hydrostatic pressure. Samples from patients with diabetes and controls were sex and age matched for daily runs. At 2 cm H2O, red blood cell transit time for the patients with diabetes was 2.73 +/- 0.05 milliseconds as compared with 2.67 +/- 0.05 milliseconds for controls (p not significant). The ratio of transit time for patients with diabetes to that of controls (Td/Tnd) was 1.03 +/- 0.01 (p less than 0.05, Wilcoxon) at 2 cm H2O and 1.02 +/- 0.01 (p not significant) at 4 cm H2O.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1989

Microvascular blood flow, volume, and velocity measured by laser Doppler techniques in IDDM.

A laser Doppler device with the capability to simultaneously measure skin blood flow, microvascular volume, and erythrocyte velocity was used to assess blood flow changes in 35 insulin-dependent diabetes mellitus (IDDM) subjects, mean age 33 +/- 1 yr, with average duration of diabetes 14 +/- 1 yr, and in a nondiabetic control group. Blood flow was determined at 35 and 44 degree C at several sites on the upper and lower extremities with a temperature-regulated probe. Blood flow was highest at both temperatures on the pulps of the index finger and the first toe, regions of high density of arteriovenous anastomoses. There was significantly greater blood flow at most locations for the nondiabetic than the diabetic group at 35 degree C, and the differences between the two groups were substantially larger at 44 degree C. At 44 degree C, blood flow in the control group was approximately 40% greater in the upper extremity and 50% greater in the lower extremity than it was in the diabetic subjects. The differences were attributed to decreases of both microvascular volume and velocity in the diabetic group. In the upper extremity, volumes in the diabetic patients were 10-15% lower and velocities 10-40% lower than in the nondiabetic subjects. In the lower extremity, volumes were 20-25% lower and velocities 40-50% lower. We conclude that laser Doppler techniques can be used to assess microvascular changes in the skin of diabetic patients. This approach may be useful to evaluate and model diabetic microangiopathy.

Adult↗

PubMed1986

Comparison and contrast of affinity chromatographic determinations of plasma glycated albumin and total glycated plasma protein.

Techniques for affinity measurement of glycated albumin and for glycated total plasma protein have been developed. The two techniques were contrasted. Both techniques are linear over a 100-fold range of sample concentrations. There appears to be a non-specific early glucose binding phase to non-albumin plasma proteins. Although this phase is detected by radioactive incorporation and thiobarbituric acid, it does not interfere with the affinity determination, which does not appear to detect the early binding species. The correlation of glycated albumin levels with glycated hemoglobin levels is much stronger than that of glycated globulin levels with glycated hemoglobin levels. Due to the large contribution of glycated albumin levels to total glycated serum protein levels, the correlation of the latter with glycated hemoglobin levels is sufficiently strong to allow the use of either technique as an adequate index of glycation.

Boronic Acids↗

PubMed1986

Clinical use and time relationship of changes in affinity measurement of glycosylated albumin and glycosylated hemoglobin.

Simple techniques for measurement of glycosylated hemoglobin and glycosylated albumin by affinity chromatography on m-aminophenylboronic acid agarose columns have recently been developed. This study explored the time course of changes in glycoalbumin versus those of glycohemoglobin in response to rapid changes in ambient glucose concentration. One would predict that glycoalbumin levels would change more rapidly than glycohemoglobin levels due to the shorter half-life of albumin than hemoglobin. This was found to be the case in a group of rabbits rendered diabetic with alloxan. Glycoalbumin levels plateaued 4 weeks after alloxan administration, while glycohemoglobin levels were still rising. In a group of diabetic patients in whom glucose levels were initially poorly controlled, strict diet or intensive insulin management were used to rapidly bring glucose levels under control. In this group of patients, the glycoalbumin values entered the normal range and plateaued, while glycosylated hemoglobin levels were still falling. Glycoalbumin determination by affinity chromatography is a valuable adjunct to glycosylated hemoglobin determination in evaluating near term control of blood sugar values.

Animals↗

PubMed1986

New screening device for assessment of peripheral neuropathy.

Screening for the onset of toxic and entrapment neuropathy is a major concern in occupational medicine today. Current perception thresholds may be used as a measure of the integrity of the peripheral nervous system. A new transcutaneous nerve stimulator was used to evaluate current perception thresholds in 54 normal persons and 33 diabetic subjects. Current perception thresholds in the normal volunteers with no evidence of peripheral neuropathy were found to vary significantly with the frequency and location of the stimulation, as well as age. The test identified the diabetic peripheral neuropathy with an overall sensitivity of 94%. This new diagnostic technique is quick, simple to perform, noninvasive and nonaversive and provides a sensitive quantitative measure of sensory function. This diagnostic stimulator will be useful for screening occupationally related toxic and entrapment neuropathies in which sensory impairment is an early finding.

Adult↗

PubMed1986

Inhibition of glycation of albumin and hemoglobin by acetylation in vitro and in vivo.

Aspirin (acetylsalicylic acid or ASA) is known to inhibit glycosylation (glycation) of albumin in vitro. The mechanism has been presumed to be acetylation, but this has never been validated. The new affinity aminophenylboronic acid procedure for determination of glycosylated albumin was used to demonstrate inhibition of glycosylation by aspirin. ASA, but not salicylic acid, inhibited glycation. The inhibition of glycation by equimolar acetic anhydride was greater than that by ASA. Pretreatment of albumin with ASA in the absence of glucose demonstrated that inhibition was extremely rapid, occurring in a matter of minutes. However, the inhibition by ASA could not be prevented by massive acceleration of glycation induced by borohydride reduction. Glycation of hemoglobin was also inhibited by ASA, but the dose requirement was considerably higher. Various analogues of ASA were evaluated for inhibition of glycation. Only acetyl-5-ethylsalicylic acid was more effective than ASA in inhibiting albumin glycation. None of these agents was more potent than ASA in inhibiting glycation of hemoglobin. ASA was fed to diabetic rats in a long-term experiment. Glycohemoglobin and glycoalbumin levels were decreased by ASA administration. We conclude that ASA inhibits glycation by a very rapid acetylation process. This process is apparently quite selective in terms of the protein involved, presumably because of the local environment of affected lysine groups. The phenomenon can be produced in vivo by administration of ASA.

Acetylation↗

PubMed1985

An interspecies comparison of normal levels of glycosylated hemoglobin and glycosylated albumin.

Aminophenylboronic acid affinity chromatography was used to measure glycosylated hemoglobin and glycosylated albumin levels in a variety of species. The highest glycosylated hemoglobin levels were found in man, the lowest in the chicken and the pig. The highest glycosylated albumin levels were found in avian species, the lowest in the mouse and the rat. A simple kinetic model was used to analyze the rates of formation of glycosylated hemoglobin and albumin in the various species. Rates of glycosylated albumin formation were very similar across the species while rates of glycosylated hemoglobin formation were quite different, presumably reflecting wide differences in erythrocyte permeability to glucose among the species.

Animals↗

PubMed1985

'Chemical hyperthyroidism': the significance of elevated serum thyroxine levels in L-thyroxine treated individuals.

We have previously reported that L-thyroxine treated patients may often have elevated serum T4 concentrations and yet show no clinical signs of hyperthyroidism. We found that such patients had normal serum T3 concentrations. The present study explored the relationship between serum T3 and T4 and dosage of L-thyroxine. Retrospective analysis of 99 patient records was performed. There was an increase of serum T4, serum T3 resin uptake (T3R), and T3 with increasing dose of L-thyroxine. The T3/T4 ratio decreased with increasing dose of L-thyroxine and with increasing T4. This phenomenon was analysed prospectively by starting 23 individuals on L-thyroxine and progressively incrementing the dose until either symptoms of hyperthyroidism developed or T4 levels exceeded the upper unit of the normal range. Once again, there was a progressive increase in serum T4, T3R, and T3 with increasing dose of L-thyroxine. At even the lowest dose of L-thyroxine (0.05 mg), there was a marked fall in T3/T4 ratio as compared to untreated individuals. The T3/T4 ratio fell further with increasing dose but with a fairly weak correlation. The decrease in T3/T4 ratio showed a much stronger correlation with serum T4. Of the 23 individuals, all exceeded the upper limit of the normal range of serum T4. No individual with elevated T4 developed clinical signs of hyperthyroidism unless serum T3 was also elevated beyond the normal range. Of eight individuals who reached elevated T3 levels, six demonstrated clinical signs of hyperthyroidism.(ABSTRACT TRUNCATED AT 250 WORDS)

Humans↗

PubMed1985

Aminophenylboronic acid affinity chromatography and thiobarbituric acid colorimetry compared for measuring glycated albumin.

Two techniques originally developed for measurement of glycated ("glycosylated") hemoglobin but also applicable to determination of glycated albumin are the thiobarbituric acid colorimetric technique (I) and the aminophenylboronic acid affinity chromatographic procedure (II). The latter reliably distinguishes diabetics from nondiabetics, and concentrations of glycated hemoglobin and glycated albumin are linearly correlated. I is nonspecific; it neither correlates with diabetic status nor with values derived via the affinity technique. Most of the chromogenic material is present in the fraction of albumin that does not bind to aminophenylboronic acid. Glucose interferes significantly with I but only slightly with II. Prolonged incubation of plasma with glucose dramatically increases the II-determined glycated albumin. Reactivity with thiobarbituric acid increases much less, and mainly in the II-bound fraction. This fraction contains a high proportion of nonspecifically reactive material. The percentage of glycated albumin determined in crude plasma samples by II differs only slightly from the value determined by purifying the albumin from the plasma. This technique appears more promising than I for eventual clinical applications.

Blood Glucose↗

PubMed1985

Use of aminophenylboronic acid affinity chromatography to measure glycosylated albumin levels.

A simple technique for the measurement of glycosylated albumin by affinity chromatography on m-aminophenylboronic acid agarose columns is presented. The technique relies on bromcresol green determination of albumin in the nonbound and bound fractions. There is a linear correlation between albumin concentration of the bound fraction and glycohemoglobin values in individuals. A control nondiabetic plasma pool with a glycohemoglobin value of 7.10% +/- 0.05% (mean +/- SEM) had a glycoalbumin value of 1.64% +/- 0.06%, while a diabetic control plasma pool with a glycohemoglobin value of 13.63% +/- 0.07% had a glycoalbumin value of 4.02% +/- 0.12%. Compared with results from the affinity technique, the preponderance of colorimetric reaction determined with the thiobarbituric acid procedure is nonspecific, in that it does not correlate with diabetic status or with values derived by the affinity procedure. The bulk of thiobarbituric acid-reactive material is present in the fraction of albumin that does not bind to aminophenylboronic acid. This nonbound fraction contains plasma glucose, which significantly interferes with thiobarbituric acid determinations but only very slightly interferes with the affinity procedure. Prolonged incubation of plasma with 500 mg/dl glucose dramatically increases affinity-determined glycosylated albumin. Thiobarbituric acid reactivity increases much less, the increase being mainly in the fraction bound to aminophenylboronic acid. The percentage glycosylated albumin determined by the affinity technique in crude plasma samples differs very slightly, if at all, from that determined by purification of the albumin from plasma. The affinity technique appears very promising for eventual clinical applications in the management of diabetes.

Blood Glucose↗

PubMed1979

A case of maturity-onset diabetes mellitus resistant to insulin but responsive to tolbutamide.

A nonobese patient with maturity-onset diabetes mellitus was hospitalized for treatment of an ulcer on his right foot. During this episode, his diabetic control worsened, and he proved unresponsive to exogenous insulin. Unresponsiveness to insulin persisted after healing of the ulcer. Tolbutamide therapy was then begun and produced a marked reduction in blood sugar levels. Withdrawal of the drug was accompanied by a progressive rise in blood sugar level. Intravenous infusion of regular pork insulin at rates of 45 U/h and single-component pork insulin at rates of 120 U/h had minimal effect on the blood sugar level. High levels of antibody to beef insulin were measured, with lower levels of pork insulin antibodies. C-peptide values were in a normal range before tolbutamide treatment and increased after use of the drug.

Administration, Oral↗

PubMed1978

Fatal compulsive water drinking.

In two cases of psychogenic polydipsia, water intoxication developed and contributed to the patient's death. The treatment of the patient with psychogenic polydipsia has been based on the presumed reversibility of the condition. Treatment of such patients must be reconsidered in light of these deaths.

Adult↗

PubMed1975

The hepatic adenylate cyclase system. I. Evidence for transition states and structural requirements for guanine nucloetide activiation.

Previous studies have shown that guanine nucleotides, acting at a site termed nucleotide regulatory site, are required for activation of hepatic adenylate cyclase and that glucagon facilitates this process. This study shows that only guanine nucleotides containing triphosphate groups at the 5' position of ribose (or 3'-deoxyribose) are capable of activating the enzyme. The terminal phosphate is not utilized in the activation process since 5'-guanylylimidodiphosphate (Gpp(NH)p and 5'-guanylyl methylenediphosphonate, analogues of GTP that are not utilized in transferase or hydrolase reactions, stimulate enzyme activity. The nucleotides bind in their free form at the regulatory site; chelation by magnesium ion shifts the apparent concentration dependence for activation by Gpp(nh)p. GDP inhibits competitively Gpp(NH)p-stimulated activity and inhibits basal activity and activities stimulated by glucagon. Activation of the enzyme by Gpp(NH)p is a slow process; the length of the lag time increases as an inverse function of nucleotide concentration and is as long as 4 min before onset of increased enzyme activity. Following pretreatment with Gpp(NH)p and extensive washing of hepatic membranes, the enzyme displays immediate increases in activity with rates that are a function of the nucleotide concentration during pretreatment; the rates remain constant for at least 6 min despite the absence of Gpp(NH)p in the medium. Studies with labeled Gpp(NH)p show that the intact nucleotide remains firmly bound to the membranes after extensive washing, suggesting that the persistence of adenylate cyclase activity may be related to slow dissociation of the nucleotide from the regulatory site. Addition of 1 nM glucagon, a submaximal concentration, does not abolish the lag phase of Gpp(NH)p activation even at saturating concentration of the nucleotide (1 muM or higher). The maximal steady state rate is achieved under these conditions. Addition of 2 muM glucagon, a saturating hormone concentration, does not alter the steady state rate but abolishes the lag phase of Gpp(NH)p activation. The transient kinetics of Gpp(NH)p activation and the effects of glucagon thereon are discussed in terms of a three state model in which the guanine nucleotide induces the formation of an intermediate transition state that displays no increase in enzyme activity over the basal state and which slowly isomerizes to a high activity state of the adenylate cyclase system; glucagon acts by accelerating the rate of isomerization.

Adenylyl Cyclases↗

PubMed1975

The hepatic adenylate cyclase system. III. A mathematical model for the steady state kinetics of catalysis and nucleotide regulation.

This paper presents a steady state kinetic model for hepatic adenylate cyclase. The activity of the enzyme has been assayed in the presence of a range of concentrations of magnesium, adenylylimidodiphosphate (App(NH)p), 5'-guanylylimidodiphosphate (Gpp(NH)p), and in the presence and absence of saturating concentrations of glucagon. The data were tested against proposed models using an iterative least squares curve fitting program (SAAM25) and confidence estimates for the model parameters were obtained. Hepatic adenylate cyclase is viewed as an enzyme having three characteristic states of catalytic function (E, E', E''). Each state has its own intrinsic activity in carrying out the catalysis of MgApp(NH)p-3 minus to form cyclic adenosine 3':5'-monophosphate. It is shown, in agreement with a proposal by de Haën, that unchelated substrate can inhibit adenylate cyclase activity. It is further concluded that this inhibition is principally due to App(NH)pH-3 minus. The three catalytic states differ markedly in their susceptibility to inhibition as well as in their Vmax, but the Km for MgApp(NH)p-2 minus is essentially the same for all states. The state transitions induced by Gpp(NH)p and by hormone are considered. Gpp(NH)p binding to state E causes transformation to state E'. State E' undergoes spontaneous transformation to state E''. Glucagon augments the transition from E' to E''. We conclude that the activating species of Gpp(NH)p is an unchelated form, most probably Gpp(NH)p-4 minus. Our results indicate that state E' is significantly more susceptible to inhibition by App(NH)pH-3 minus than the other two states. Certain phenomena occurring in fat cell adenylate cyclase are discussed in light of our findings in hepatic adenylate cyclase.

Adenine Nucleotides↗

PubMed1975

The hepatic adenylate cyclase system. II. Substrate binding and utilization and the effects of magnesium ion and pH.

The kinetic characteristics of substrate utilization by hepatic adenylate cyclase were investigated under a variety of incubation conditions, including veriations in pH, [substrate], [Mg2+], and in the absence or presence of glucagon. Activities were compared with ATP and 5'-adenylylimidodiphosphate (App(NH)p) as substrates. The Km for both substrates was about 50 muM; Vmax given with App(NH)p was about 40% lower than obtained with ATP as substrate. In the presence of a saturating concentration of substrate (1 mM), basal activity was increased 4-fold by increasing [Mg2+] from 5 to 50 mM. The stimulatory effect of Mg2+ was not due to an allosteric action since basal activity was only marginally enhanced (40%) when the substrate concentration was reduced to 10 muM. As suggested by deHaen ((1974 J. Biol. Chem. 249, 2756), it is likely that Mg2+ increases enzyme activity by decreasing the concentration of an inhibitory, unchelated form of substrate that competes with the productive magnesium-substrate complex at the active site. Activity-pH profiles differed with ATP and App(NH)p as substrates; a shift in pH optimum was observed which correlated with the different pKa of the terminal phosphate groups of ATP and App(nh)p, and which reflect the concentration of protonated substrate (ATPH-3 minus) present in the incubation medium. Accordingly, protonated substrate is the predominant inhibitory species of unchelated substrate and probably has a considerably higher affinity for the active site than does the magnesium-substrate complex. Glucagon-stimulated activity was less susceptible to inhibition by protonated substrate than is the basal state as evidenced by lower stimulatory effect when the [Mg2+] was increased from 5 to 20 mM. However, increasing the [Mg2+] from 20 to 50 mM resulted in marked inhibition of glucagon-stimulated activity, particularly in the presence of 10 muM substrate. Conversely, at a fixed [Mg2+], concentrations of substrate at least 20-fold higher than the Km were required to achieve maximal hormone-stimulated activity. These findings suggest that the unchelated, fully ionized form of substrate serves as an activating ligand, as has been observed with guanine nucleotides at considerably lower concentrations. Thus, Mg2+ affects adenylate cyclase activity by forming the productive substrate complex and by titrating the inhibitory protonated and activating free forms of substrate. As a result of these effects of unchelated substrate, it proved difficult to evaluate the kinetic parameters involved in substrate binding and utilization and the effects of hormone thereon when substrate was added as the only source of activating ligand. However, linear Michaelis kinetic data were obtained by adding the activating ligand 5'-guanylylimidodiphosphate with glucagon and by making appropriate adjustments of pH and [Mg2+]. Vmax was increased 4-fold without changes in Km by the actions of 5'-guanylylimidodiphosphate and glucagon.

Adenine Nucleotides↗