Biomedical subjects
Publications and source records attributed to B H Robinson.
Molecular dynamics have been studied by saturation transfer EPR. Rotational correlation times are obtained from the quadrature signal, as a ratio of spectral intensities at different field positions. It is possible to define ratio parameters that are independent of the phase of the modulation, but that can reduce to ratio parameters previously defined.
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Two patients with biotin-responsive multiple carboxylase deficiency, both presenting with predominant lactic acidosis, are reported. One with disease of early neonatal onset had considerable acute neurologic and persistent dermatologic abnormalities. The other, with late juvenile-onset disease, had chronic neurologic abnormalities without dermatologic findings. Early-onset cases generally have been associated with holocarboxylase synthetase deficiency, whereas those of juvenile onset have been characterized as representing defects in intestinal biotin absorption. However, enzyme analyses of fibroblasts from both patients, grown in biotin-deficient medium, revealed markedly diminished activities of pyruvate, propionyl-CoA, and beta-methylcrotonyl-CoA carboxylases, and all three enzymes showed normal activities after growth in biotin-rich medium. Furthermore, lymphoblast enzyme analysis in the patient with disease of early onset had previously revealed a defect in holocarboxylase synthetase, and fibroblast complementation studies showed that both patients belong to the bio complementation group. These findings indicate that considerable clinical heterogeneity exists among patients with holocarboxylase synthetase deficiency, an observation which does not permit differentiation of the biochemical forms of multiple carboxylase deficiency on the basis of age at onset and clinical presentation.
A 6-month-old girl with vomiting, hypotonia and motor retardation was found to have elevated blood lactate, pyruvate, and branched chain amino acids associated with ketoglutaric aciduria. The combination of a congenital lactic acidosis with a variant form of maple syrup urine disease and ketoglutaric aciduria suggested a defect of a single component, common to pyruvate dehydrogenase, to branched chain ketoacid dehydrogenase, and to alpha-ketoglutarate dehydrogenase. Dihydrolipoyl dehydrogenase is the common component (E3). The three enzyme activities and the E3 component activity were found to be reduced in liver and cultured fibroblasts, thus confirming that a single defect of this component can result in a multiple deficiency involving several oxidative decarboxylation reactions.
An Irish family with an unusual periodic syndrome is described. Attacks consist of fever with localized myalgia and painful erythema. Other features include abdominal pain and pleurisy, with leucocytosis and a high ESR. The syndrome resembles classical familial Mediterranean fever (FMF) but differs from it in its prompt response to steroids and its autosomal dominant pattern of inheritance. The disease appears to have a benign course and no patient has developed amyloid.
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Two unrelated Canadian Indian infants presented with metabolic acidosis. Lactate, pyruvate, glutamic acid, proline and alanine were greatly elevated in plasma. Urinary excretion of alpha-ketoglutarate and pyruvate was increased. Pyruvate carboxylase activity was very low in skin fibroblasts and liver. Phosphoenolpyruvate carboxykinase was low in liver. Both infants were unresponsive to several enzyme cofactors, including biotin. Both survive at age 2 years with severe mental retardation..
The resolution and sensitivity of electron paramagnetic resonance (EPR) and saturation transfer EPR (ST-EPR) for biological applications are greatly improved by deuteration and substitution of (15)N for (14)N in the spin-labeled probe N-(1-oxyl-2,2,6,6-tetramethyl-4-piperidinyl)maleimide (MSL). The EPR and ST-EPR spectra of the deuterated analogue [(2)H]MSL and the (15)N-substituted and deuterated derivative [(15)N, (2)H]MSL were compared with those of the parent MSL. The [(15)N, (2)H]MSL showed the greatest gain in sensitivity and the most marked sharpening of spectral features. These improvements were due to (i) a reduction in the spectral linewidths resulting from the relatively weak hyperfine interactions of the unpaired electron with deuterium and (ii) spectral simplification due to a reduction in the number of nuclear manifolds from three to two in replacing (14)N with (15)N. In the freely tumbling state, the spectra of [(15)N, (2)H]MSL and [(2)H]MSL showed 10-fold and 5-fold increases, respectively, in signal heights compared to MSL. To study the slow tumbling frequencies characteristic of biological molecules, the MSL and its derivatives were covalently bound to the enzyme glyceraldehyde-3-phosphate dehydrogenase [GAPDHaase; D-glyceraldehyde-3-phosphate:NAD(+) oxidoreductase (phosphorylating), EC 1.2.1.12] on cysteine-149 of the catalytic site. The EPR and ST-EPR spectra of [(15)N, (2)H]MSL and [(2)H]MSL adducts showed 3- and 1.5-fold gains in sensitivity, respectively. More important, there were striking increases in resolution, particularly for [(15)N, (2)H]MSL over MSL. These improvements were observed throughout the correlation time range from 0.1 musec to 1 msec. The EPR spectrum of [(15)N, (2)H]MSL-GAPDHase at X-band showed no overlap of the two nuclear manifolds; therefore, all the elements of the A and g tensors could be measured directly from the spectrum. The increase in sensitivity and resolution of the (15)N- and deuterium-substituted spin labels permitted quantitative simulation of the EPR and ST-EPR spectra of a labeled protein. Computation time was reduced 90% by (15)N substitution. Use of (15)N-substituted and deuterated spin probes substantially improved characterization of the motional properties of a protein.
Binding of the glycolytic enzyme, glyceraldehyde-3-phosphate dehydrogenase [GAPDHase; D-glyceraldehyde-3-phosphate:NAD+ oxidoreductase (phosphorylating EC 1.2.1.12], to the cytoplasmic segment of band-3 protein in the erythrocyte (RBC) membrane has been examined by electron paramagnetic resonance (EPR) and saturation transfer EPR (ST-EPR) spectroscopies. GAPDHase, which was isolated from rabbit muscle and labeled with the resolution-enhancing deuterated N-(15N-1-oxyl-2,2,6,6-tetramethyl-4-piperidinyl)maleimide spin label ([15N,2H]MSL), showed the same binding specificity for the transmembrane band-3 protein of human erythrocyte membranes as reported for unlabeled GAPDHase from human RBC. Experimental EPR lineshapes from soluble and membrane-bound enzymes were analyzed by direct stimulation of spectra and indicated a structural alteration of the bound GAPDHase in the vicinity of the spin label, which was attached covalently to the active-site cysteine-149 residue. A rigorous theoretical analysis of the ST-EPR spectra of soluble and membrane-bound enzyme is presented and utilized in conjunction with model system analysis to demonstrate that the motion of membrane-bound GAPDHase could be characterized by an effective isotropic rotational correlation time of 20 microseconds. This indicated that the GAPDHase--band-4 complex exhibits motional freedom relative to the membrane-spanning segment of the band-3 protein or the RBC. The double substituted spin label [15N,2H]MSL affords gains in sensitivity and resolution that permit studies of membrane-bound enzymes at physiological levels and quantitative simulations of the EPR and ST-EPR lineshapes with reasonable computation times.
The long-term effects of vitamin D analogues and metabolites on renal function were assessed in 24 patients with and without chronic renal failure. Treatment for periods of 5-45 months did not adversely affect renal function in 10 of 11 patients with stable renal function, although transient hypercalcaemia did cause transient rises in plasma creatinine. Of 13 patients with progressive renal failure before treatment, vitamin D-like compounds or the vehicle used for their administration may have accelerated renal failure in 3 patients independently of changes in plasma calcium or phosphate. Particular difficulties in assessing the effects of vitamin D-like compounds in progressive renal disease are discussed.
The incidence of cancer and related mortality was studied in 1651 patients from six dialysis centres in England over 10 years. The only type of cancer for which there was a significant excess was non-Hodgkin's lymphoma (four cases observed against an expected incidence of 0.15 (p < 0.001); three deaths against an expected 0.1 (p < 0.001)). This excess could not be attributed to either subsequent transplantation or treatment with immunosuppressive drugs. Since immunodepression is a feature of chronic renal failure, these observations together with those on patints treated with immunosuppressive drugs suggest that immunosuppression favours the development of non-Hodgkin's lymphoma. Studies in which it is concluded that patients receiving dialysis show an excess of other types of cancer have certain shortcomings; the unusual opportunities for detecting cancer in such patients may account for some of the reported excess.
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Two patients on long-term lithium therapy for manic-depressive psychosis developed serious toxicity within days of being prescribed a combination of triamterene (50 mg) and hydrochlorothiazide (25 mg) for mild symptomless hypertension. Reduced clearance of lithium has been reported to follow its concurrent administration with diuretics that deplete both sodium and potassium. A combination of triamterene with thiazide has not been shown previously to precipitate lithium toxicity.
The rate of glucose turnover (RT) has been studied in 33 subhuman primate newborn (Macaca mulatta). There appears to be a linear relationship between RT and plasma glucose (G) such that RT = 1.053 G + 0.242. Liver enzymes show a change in specificity such that hexokinase is predominant in the preterm animals and glucokinase has little activity, while in the term animal these enzymes of of equal activity. In the 1-year-old animal glucokinase predominates. Hexokinase activity in the brain remains constant throughout development. These results imply that low blood glucose in the neonate is not associated with increased glucose utilization.
The capacity for gluconeogenesis has been studied in 33 subhuman primate newborn (Macaca mulatta) in the basal steady state. Basal blood glucose levels were seen to rise with increasing postnatal age. Availability of the major gluconeogenic substrates, alanine and lactate, was adequate at times when blood glucose and the rate of gluconeogenesis were low. Hepatic and renal cortical content of the four key gluconeogenic enzymes was low during the 1st week of life compared to adult levels. Diminished induction of the gluconeogenic enzymes did not appear to be the cause of low blood glucose levels. The serum-free fatty levels were directly correlated to both the basal glucose levels and to the rate of gluconeogenesis.
A total of 40 skin fibroblast cultures from pediatric cases of lactic acidosis were subjected to a series of tests designed to elucidate the nature of an underlying defect in metabolism. Of these 40 cases, in 14 we were able to define the following problems. Pyruvate carboxylase deficiency was evident in five cases showing < 10% normal activity. Phosphoenolpyruvate carboxykinase deficiency was evident in one case where the whole cells showed 17% of normal activity whereas the mitochondrial activity of this enzyme was 6% of normal. Pyruvate dehydrogenase deficiency was present in six cases showing 8 to 39% of normal activity, five of them being due to deficient pyruvate decarboxylase activity and one of them being due to deficient dihydrolipoyl dehydrogenase activity. Two cases were found with normal enzymes of pyruvate metabolism in which the production of 14CO2 from [3-14C]pyruvate was deficient at 13 and 28% of normal activity, respectively, which we consider to be indicative of reduced activity of the Krebs' cycle. The grounds for the diagnosis of these 14 affected cases are documented, and the clinical presentation of these enzyme deficiencies is assessed in the light of present knowledge about lactic acidosis.
A 2-year-old boy had acute fever, malaise, and somnolence with hepatomegaly, increased blood ammonia content (338 microM), high SGOT, low blood glucose content, and mild acidosis. A liver biopsy showed diffuse accumulation of lipid droplets in swollen hepatocytes, and abnormal urinary metabolites included beta-hydroxy-beta-methyl glutarate (HMG), beta-methylglutaconate, beta-hydroxyisovalerate, and beta-methylglutaric and glutaric acids. In cultured skin fibroblasts and liver, beta-hydroxy-beta-methyl glutaryl CoA lyase activity was about 10% of normal. Therefore, a genetic deficiency of HMGCoA lyase activity can cause a clinical syndrome similar to that of Reye syndrome when the patient is stressed by an acute viral infection.