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C Ho

Publications and source records attributed to C Ho.

At least 37 records · Page 2Linked to original sources
PubMed1991

Roles of the beta 146 histidyl residue in the molecular basis of the Bohr effect of hemoglobin: a proton nuclear magnetic resonance study.

Assessment of the roles of the carboxyl-terminal beta 146 histidyl residues in the alkaline Bohr effect in human normal adult hemoglobin by high-resolution proton nuclear magnetic resonance spectroscopy requires assignment of the resonances corresponding to these residues. Previous resonance assignments in low ionic strength buffers for the beta 146 histidyl residue in the carbonmonoxy form of hemoglobin have been controversial [see Ho and Russu (1987) Biochemistry 26, 6299-6305; and references therein]. By a careful spectroscopic study of human normal adult hemoglobin, enzymatically prepared des(His146 beta)-hemoglobin, and the mutant hemoglobins Cowtown (beta 146His----Leu) and York (beta 146His----Pro), we have resolved some of these conflicting results. By a close incremental variation of pH over a wide range in chloride-free 0.1 M N-(2-hydroxyethyl)piperazine-N'-2-ethanesulfonic acid buffer, a single resonance has been found to be consistently missing in the proton nuclear magnetic resonance spectra of these hemoglobin variants. The spectra of each of these variants show additional perturbations; therefore, the assignment has been confirmed by an incremental titration of buffer conditions to benchmark conditions, i.e., 0.2 M phosphate, where the assignment of this resonance is unambiguous. The strategy of incremental titration of buffer conditions also allows extension of this resonance assignment to spectra taken in 0.1 M [bis(2-hydroxyethyl)amino]tris(hydroxymethyl)methane buffer. Participation of the beta 146 histidyl residues in the Bohr effect has been calculated from the pK values determined for the assigned resonances in chloride-free 0.1 M N-(2-hydroxyethyl)piperazine-N'-2-ethanesulfonic acid buffer. Our results indicate that the contribution of the beta 146 histidyl residues is 0.52 H+/hemoglobin tetramer at pH 7.6, markedly less than the 0.8 H+/hemoglobin tetramer estimated by study of the mutant hemoglobin Cowtown (beta 146His----Leu) by Shih and Perutz [(1987) J. Mol. Biol. 195, 419-422]. We have found that at least two histidyl residues in the carbonmonoxy form of this mutant have pK values that are perturbed, and we suggest that these pK differences may in part account for this discrepancy. Furthermore, summation of the positive contribution of the beta 146 histidyl residues and the negative contribution of the beta 2 histidyl residues to the maximum Bohr effect measured in 0.1 M N-(2-hydroxyethyl)piperazine-N'-2-ethanesulfonic acid buffer suggests that additional sites in the hemoglobin molecule account for proton release upon ligation greater than the contribution of the beta 146 histidyl residues.(ABSTRACT TRUNCATED AT 400 WORDS)

Hemoglobin A↗
PubMed1991

An evaluation of the integrity of the blood-testis barrier by magnetic resonance imaging.

This present investigation was initiated to noninvasively evaluate the usefulness of intravenous gadopentetate dimeglumine (Gd-PTDM)-enhanced magnetic resonance imaging (MRI) in assessing the integrity of the blood-testis barrier (BTB). The intensity of different image slices was measured in pre- and post-Gd-PTDM images in rats receiving cytochalasin D or alcohol treatment. It was found that MRI can be used to assess the integrity of the BTB and may be a useful tool in the evaluation of potentially toxic agents that affect the testis, particularly those that affect the BTB.

Animals↗
PubMed1991

Cyclosporine and liver regeneration studied by in vivo 31P nuclear magnetic resonance spectroscopy.

The changes in fructose-1-phosphate (F-1-P), intracellular pH, and ATP content of the liver after a fructose challenge were investigated noninvasively in vivo using phosphorus-31 nuclear magnetic resonance spectroscopy of dog liver four days after a portacaval shunt (PCS) with or without portal venous infusion of cyclosporin (CsA). The F-1-P metabolism was slower in PCS dogs (N = 2) as compared to either the normal (N = 2) or PCS + CsA-treated dogs (N = 3) (P less than 0.05). The intracellular pH temporarily decreased from 7.3 +/- 0.05 to 7.0 +/- 0.05 during the fructose challenge. The regenerative indexes were increased in the PCS + CsA group (P less than 0.01). These data obtained in vivo using 31P-NMR spectroscopy in the liver following a portacaval shunt, suggest that: (1) the energy status of the liver and the metabolic response to fructose are reduced in PCS compared to normal animals and (2) CsA treatment enhances the regenerative response of the liver and prevents the reduction in hepatic function associated with portacaval shunting.

Acid-Base Equilibrium↗
PubMed1991

Resolution of fluorescence intensity decays of the two tryptophan residues in glutamine-binding protein from Escherichia coli using single tryptophan mutants.

Time correlated single photon counting measurements of tryptophan (Trp) fluorescence intensity decay and other spectroscopic studies were performed on glutamine-binding protein (GlnBP) from Escherichia coli. Using site-specifically mutated forms of the protein in which tyrosine (Tyr) and phenylalanine (Phe) substitute for the Trp residues at positions 32 and 220, we have examined whether wild-type (Wtyp) intensity decay components may be assigned to specific Trp residues. Results indicate that: (a) two exponential intensity decay components are recovered from the Wtyp protein (6.16 ns, 0.46 ns); (b) the long decay component arises from Trp-220 and comprises greater than 90% of the total fluorescence emission; (c) the short component arises from Trp-32 and is highly quenched; (d) all four single-Trp mutants exhibit multiexponential intensity decays, yet equimolar mixtures of two single-Trp mutants yield only two decay components which are virtually indistinguishable from the Wtyp protein; (e) the recovery of additional components in protein mixtures is obscured by statistical noise inherent in the technique of photon counting; (f) various spectroscopic measurements suggest that Trp-Trp interactions occur in the Wtyp protein, but the Wtyp intensity decay may be closely approximated by a linear combination of intensity decays from single-Trp mutants; and (g) inferences derived independently from fluorescence and NMR spectroscopy which pertain to the presence of Trp-Trp interactions and the relative solvent exposure of the two Trp residues are in agreement.

Amino Acid Sequence↗
PubMed1991

Mutagenic DNA repair in enterobacteria.

Sixteen species of enterobacteria have been screened for mutagenic DNA repair activity. In Escherichia coli, mutagenic DNA repair is encoded by the umuDC operon. Synthesis of UmuD and UmuC proteins is induced as part of the SOS response to DNA damage, and after induction, the UmuD protein undergoes an autocatalytic cleavage to produce the carboxy-terminal UmuD' fragment needed for induced mutagenesis. The presence of a similar system in other species was examined by using a combined approach of inducible-mutagenesis assays, cross-reactivity to E. coli UmuD and UmuD' antibodies to test for induction and cleavage of UmuD-like proteins, and hybridization with E. coli and Salmonella typhimurium umu DNA probes to map umu-like genes. The results indicate a more widespread distribution of mutagenic DNA repair in other species than was previously thought. They also show that umu loci can be more complex in other species than in E. coli. Differences in UV-induced mutability of more than 200-fold were seen between different species of enteric bacteria and even between multiple natural isolates of E. coli, and yet some of the species which display a poorly mutable phenotype still have umu-like genes and proteins. It is suggested that umDC genes can be curtailed in their mutagenic activities but that they may still participate in some other, unknown process which provides the continued stimulus for their retention.

Blotting, Southern↗
PubMed1991

Knee hyaline cartilage evaluated with MR imaging: a cadaveric study involving multiple imaging sequences and intraarticular injection of gadolinium and saline solution.

Magnetic resonance (MR) imaging of cadaveric knees was performed to determine optimal sequences for visualization of hyaline cartilage. Six fresh-frozen cadaveric knees were imaged with a 1.5-T imager by means of standard and hybrid fat suppression (HFS) spin-echo techniques, with and without intraarticular injection of saline solution and gadopentetate dimeglumine. The knees then were sectioned at 4-mm intervals. Both the real and the imaged cartilage thicknesses were measured. Areas of cartilage thinning and focal defects seen in the cadaveric sections were most accurately matched, in both the presence and the absence of intraarticular saline solution simulating joint fluid, by images obtained with the T1-weighted HFS sequences. Accurate imaging of hyaline cartilage thickness with differentiation of cartilage from fluid was possible routinely. Standard and HFS spin-echo images obtained after intraarticular injection of gadopentetate dimeglumine depicted cartilage less accurately than HFS sequences either with or without saline injection. MR imaging with T1-weighted HFS sequences provided superior visualization of cartilage, enabling accurate measurements of cartilage thickness and differentiation of cartilage from saline solution simulating joint fluid.

Cartilage, Articular↗
PubMed1991

Medial dislocation of the biceps brachii tendon: appearance at MR imaging.

Abnormalities of the long tendon of the biceps brachii muscle commonly accompany other lesions about the shoulder, especially rotator cuff rupture, and are a frequent cause of a painful shoulder. The spectrum of abnormalities associated with medial displacement of the biceps tendon seen at magnetic resonance (MR) imaging was reviewed in six patients. MR imaging was performed on a 1.5-T system with use of a dedicated surface coil. The findings at MR imaging were correlated with those at surgery. Two types of medial displacement of the biceps tendon were identified. More frequently observed was a defect in the subscapularis apparatus that allowed intraarticular entrapment of the biceps tendon. Less commonly observed was incomplete dislocation, with the biceps tendon lying between a partially disrupted subscapularis tendon. MR imaging enabled accurate identification of medial dislocation of the biceps tendon and entrapment of the tendon within the glenohumeral joint. MR imaging also demonstrated the associated disruption of the subscapularis tendon that must be present to allow the biceps tendon access to the joint space.

Aged↗
PubMed1991

Effect of cyclosporine on hepatic energy status and on fructose metabolism after portacaval shunt in dog as monitored by phosphorus-31 nuclear magnetic resonance spectroscopy in vivo.

The effect of cyclosporin A on the hepatic energy status and intracellular pH of the liver and its response to a fructose challenge has been investigated using in vivo phosphorus-31 nuclear magnetic resonance spectroscopy in dogs. Three experimental groups were studied: (a) control dogs (n = 5), (b) dogs 4 days after the creation of an end-to-side portacaval shunt (n = 5), and (c) dogs 4 days after portacaval shunt and continuous infusion of cyclosporin A (4 mg/kg/day) by way of the left portal vein (portacaval shunt plus cyclosporin A, n = 5). The phosphorus-31 nuclear magnetic resonance spectra were obtained at 81 MHz using a Bruker BIOSPEC II 4.7-tesla nuclear magnetic resonance system equipped with a 40-cm horizontal bore superconducting solenoid. The phosphomonoesters (p less than 0.01), inorganic phosphate and ATP levels (p less than 0.05) were decreased significantly in portacaval shunt-treated and in portacaval shunt-plus-cyclosporin A-treated dogs compared with unshunted control dogs. After a fructose challenge (750 mg/kg body wt, intravenously), fructose-1-phosphate metabolism was reduced in portacaval shunt-treated dogs compared with either the normal or portacaval shunt-plus-cyclosporin A-treated dogs (p less than 0.05). Both portacaval shunt- and portacaval shunt-plus-cyclosporin A-treated dogs demonstrated a reduced decline in ATP levels after fructose infusion when compared with the controls (p less than 0.05). Immediately after the fructose challenge, the intracellular pH decreased from 7.30 +/- 0.03 to 7.00 +/- 0.05 in all animals (p less than 0.01) and then gradually returned to normal over 60 min.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1990

1H and 31P nuclear magnetic resonance investigation of the interaction between 2,3-diphosphoglycerate and human normal adult hemoglobin.

High-resolution 1H and 31P nuclear magnetic resonance spectroscopy has been used to investigate the binding of 2,3-diphosphoglycerate to human normal adult hemoglobin and the molecular interactions involved in the allosteric effect of the 2,3-diphosphoglycerate molecule on hemoglobin. Individual hydrogen ion NMR titration curves have been obtained for 22-26 histidyl residues of hemoglobin and for each phosphate group of 2,3-diphosphoglycerate with hemoglobin in both the deoxy and carbonmonoxy forms. The results indicate that 2,3-diphosphoglycerate binds to deoxyhemoglobin at the central cavity between the two beta chains and the binding involves the beta 2-histidyl residues. Moreover, the results suggest that the binding site of 2,3-diphosphoglycerate to carbonmonoxyhemoglobin contains the same (or at least some of the same) amino acid residues responsible for binding in the deoxy form. As a result of the specific interactions with 2,3-diphosphoglycerate, the beta 2-histidyl residues make a significant contribution to the alkaline Bohr effect under these experimental conditions (up to 0.5 proton/Hb tetramer). 2,3-Diphosphoglycerate also affects the individual hydrogen ion equilibria of several histidyl residues located away from the binding site on the surface of the hemoglobin molecule, and, possibly, in the heme pockets. These results give the first experimental demonstration that long-range electrostatic and/or conformational effects of the binding could play an important role in the allosteric effect of 2,3-diphosphoglycerate on hemoglobin.(ABSTRACT TRUNCATED AT 250 WORDS)

Diphosphoglyceric Acids↗
PubMed1990

Site-specific incorporation of 5-fluorotryptophan as a probe of the structure and function of the membrane-bound D-lactate dehydrogenase of Escherichia coli: a 19F nuclear magnetic resonance study.

The structure and function of the membrane-bound D-lactate dehydrogenase of Escherichia coli have been investigated by fluorine-19 nuclear magnetic resonance spectroscopy of 5-fluorotryptophan-labeled enzyme in conjunction with oligonucleotide-directed, site-specific mutagenesis. 5-Fluorotryptophan has been substituted for nine phenylalanine, tyrosine, and leucine residues in the enzyme molecule without loss of activity. The 19F signals from these additional tryptophan residues have been used as markers for sensitivity to substrate, exposure to aqueous solvent, and proximity to a lipid-bound spin-label. The nuclear magnetic resonance data show that two mutational sites, at amino acid residues 340 and 361, are near the lipid environment used to stabilize the enzyme. There are a number of amino acid residues on the carboxyl side of this region that are strongly sensitive to the aqueous solvent. The environment of the wild-type tryptophan residue at position 469 changes as a result of two of the substitution mutations, suggesting some amino acid residue-residue interactions. Secondary structure prediction methods indicate a possible binding site for the flavin adenine dinucleotide cofactor in the carboxyl end of the enzyme molecule. These results suggest that the membrane-bound D-lactate dehydrogenase may have the two-domain structure of many cytoplasmic dehydrogenases but with the addition of a membrane-binding domain between the catalytic and cofactor-binding domains. This type of three-domain structure may be of general significance for understanding the structure of membrane-bound proteins which do not traverse the lipid bilayer of membranes.

Amino Acid Sequence↗
PubMed1990

Absence of pH changes during altered work in the in vivo sheep heart: a 31P-NMR investigation.

Saturation transfer from gamma-ATP to inorganic phosphate was used to assign the intracellular inorganic phosphate resonance of the phosphorus-31 nuclear magnetic resonance spectrum of heart obtained from adult sheep under Halothane anesthesia. The 31P chemical shift of intracellular inorganic phosphate was then used as a probe of myocardial pH. Resting myocardial pH was found to be 7.03 +/- 0.02. The effects of increasing myocardial work on myocardial pH were examined using external pacing and phenylephrine infusion alone or in combination to produce steady-state increases in the rate-pressure product. No alteration in myocardial pH was observed with up to 4-fold increases in rate-pressure product. No changes in high-energy phosphates were observed except at the highest rate-pressure products obtained, where small increases in inorganic phosphate and decreases in the phosphocreatine/ATP ratio were observed. In addition, the transition to a new steady state was studied with a 20-s time resolution after initiation of pacing. Again, no changes in pH or levels of phosphates were detected during the transition to increased work.

Adenosine Triphosphate↗
PubMed1990

Pharmacokinetics of cefpodoxime in young and elderly volunteers after single doses.

Three pharmacokinetic studies involving single oral doses of cefpodoxime proxetil in healthy volunteers are reported. The first study was to determine the absolute bioavailability of cefpodoxime, the second was to study the relationship between the oral dose of cefpodoxime proxetil and pharmacokinetic parameters of cefpodoxime, and the third was to compare the pharmacokinetics of cefpodoxime in healthy young and elderly volunteers. Half the dose of cefpodoxime orally administered as cefpodoxime proxetil in tablet form reaches the systemic circulation, while 80% of the cefpodoxime absorbed is excreted unchanged in urine. The volume of distribution is large (32.3 l). The pharmacokinetics of cefpodoxime were linear in young and elderly subjects after 100 and 200 mg oral doses, which are those used therapeutically. The Cmax was about 1.4 mg/l (after 100 mg) and 2.6 mg/l (after 200 mg). Deviation from linearity appeared at 400 mg and the effect was confirmed at 800 mg. The differences between young and elderly subjects were negligible, with the exception of the half-life which increased by only 14%, from 2.67 to 3 h. Dosage adjustment is therefore not necessary in the elderly.

Administration, Oral↗
PubMed1990

Brain pH in acute isocapnic metabolic acidosis and hypoxia: a 31P-nuclear magnetic resonance study.

It is well known that brain pH changes rapidly in acute hypercapnia or hypocapnia. The effect of acute isocapnic metabolic acid-base change on brain pH is less certain. To study this problem, acute isocapnic metabolic acidosis was induced by HCl or lactic acid infusions in rats, and recovery from acidosis was accomplished by NaHCO3 infusion. Brain pH was measured by 31P-nuclear magnetic resonance. Despite decreases in blood pH of 0.34 and 0.36 units, respectively, in less than 1 h of acid infusion and rapid recovery during bicarbonate infusion, brain pH was unaffected (ranging between 7.08 and 7.11) and was uncorrelated with blood pH. The blood pH minus brain pH gradient was eliminated by the acidosis. By contrast, hypoxia-induced endogenous lactic acidosis lowered blood and brain pH equivalently, but the fall in brain pH preceded that in blood. During normoxic recovery, brain pH overshot and became alkaline when blood pH was still significantly reduced and blood lactate levels were markedly elevated. Presumably, this is due to stimulated active H+ transport. The results demonstrate that brain pH is affected differently in metabolic, respiratory, and endogenous acid-base disturbances. Thus brain pH cannot be predicted solely from blood pH values.

Acid-Base Imbalance↗
PubMed1990

Jogging causes acute changes in the knee joint: an MR study in normal volunteers.

As MR imaging allows evaluation of soft-tissue structures not previously possible with imaging techniques, we undertook a preliminary study to evaluate the effects of a popular form of exercise (jogging) on the knee. The specific question prompting our investigation was, does repetitive impulse loading produced by jogging cause acute structural changes within the knee that are visible by MR imaging? The knees of 10 healthy subjects were examined on a 1.5-T MR system before and immediately after 30 min of continuous jogging. The same extremity was examined each time, and the imaging sequences and photographic technique (meniscal windows) were identical for both examinations. Effusions developed in five of 10 subjects after exercise. In addition, five of 10 subjects had subtle increased signal intensity within their menisci. These results suggest that jogging frequently leads to acute changes in the knee that are visible on MR imaging. The significance of these changes is unknown.

Acute Disease↗