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Biomedical subjects

M Cohn

Publications and source records attributed to M Cohn.

At least 163 records · Page 9Linked to original sources
PubMed1980

Shift of the equilibrium constant of the 3-P-glycerate kinase reaction towards 1,3-bis-P-glycerate with adenosine 5'-O-(2-thiotriphosphate) (ATP beta S) as substrate.

It has been demonstrated that the reaction of ATP beta S and 3-P-glycerate catalyzed by 3-P-glycerate kinase, unlike the reaction with ATP, can form a readily detectable amount of 1,3-bis-P-glycerate as observed by 31P NMR. By quantifying production of 1,3-bis-P-glycerate from the phosphorothioate analogue of ATP as a function of time as the reaction approaches equilibrium, Keq for the reaction was estimated to be approximately 400, about 1 order of magnitude less than the equilibrium constant previously reported for the analogous reaction of the normal nucleotide substrates.

Adenosine Triphosphate↗
PubMed1979

Determination of the kappa anti-alpha(1,3) dextran immune response difference by A gene(s) in the VKappa-locus of mice.

Mice lacking the V(alpha(1,3) (h gamma1)-gene do not produce a gamma1 anti-alpha(1,3) dextran response. However, on hyperimmunization some strains mount a kappa-anti-alpha(1,3) dextran response, whereas other remain nonresponder. Responsiveness in dominant. The kappa-anti-alpha(1,3) response difference is linked to the Ly-3 locus on chromosone 6 and is likely the result of a structural Vkappa-gene(s). In conjunction with previous work, three Vkappa-allogroups can now be distinguished. At present, this is the only example of an immune responsiveness difference associated with the Vkappa-locus.

Animals↗
PubMed1979

Methionyl-tRNA synthetase of Escherichia coli. A zinc metalloprotein.

The native dimeric form of methionyl-tRNA synthetase of Escherichia coli contains two zinc atoms per dimer, one per subunit. The bound zinc is retained upon trypsin modification which yields a monomer with one zinc atom. The enzymatic activity of both the dimeric forms is reversibly inhibited by 1,10-phenanthroline but not by its non-chelating analogues. In addition, the native enzyme binds two Mn2+ per dimer with a binding constant of approx. 70 micron but no binding is observed with the trypsin-modified monomer.

Amino Acyl-tRNA Synthetases↗
PubMed1979

Steroids and immunosuppression. Effect on anastomotic intimal hyperplasia in femoral arterial dacron bypass grafts.

The effects of steroids and immunosuppression on 6-cm long bilateral femoral arterial Dacron bypass grafts were studied in 30 adult mongrel dogs. The dogs were serially placed into one of the following three groups: control, steroid, and immunosuppression. The control and steroid groups each had a 70% graft patency rate, whereas the immunosuppression group had a 100% eight-week graft patency rate. The results in the steroid group were not statistically different from the control group, whereas the results in the immunosuppression group were statistically different from the control. The decrease in internal diameter was secondary to a localized accumulation of tissue at the anastomotic site, which histologically appeared to be a hyperplastic intima morphologically different in each group. There is a substantial decrease in intimal hyperplasia at anastomotic sites and a higher graft patency rate in dogs treated with low-dose azathioprine as compared with control of steroid-treated animals. The mechanism seems to be a slower and more orderly intimalization rather than suppression of any specific intimal cellular elements.

Animals↗
PubMed1978

On a regulatory gene controlling the expression of the murine lambda1 light chain.

We describe here two alleles, an allele of the lambda1 locus present in the SJL strain (rlambda1lo) and an allele of the lambda1 locus present in the BALB/c strain (rlambda1 +), of a regulatory gene locus which specifically influences the expression of the mouse lambda1 light chain structural gene. The rlambda1 regulatory gene is not linked to either the major histocompatibility complex or to the heavy-chain allogroup but appears to be linked to the lambda1 structural gene locus. In the homozygous state, the present of the rlambda1lo allele results in a 50-fold reduction in the number of lambda1 antigen-sensitive, bone-marrow derived lymphocytes (ASCs) compared to the presence of the rlambda1 + allele. However, those few lambda1ASCs present in rlambda1lo homozygotes can be induced normally to produce lambda1 light chains indistinguishable from those found in rlambda1 + homozygotes. The reduction in lambda1ASC's due to the rlambda1lo allele results both in a reduction in the amount of lambda1 Ig in the serum and also in a large variation in the magnitude of the lambda1 antibody response to alpha(1,3) dextran by individual animals. This variation permits the estimate that, on the average, 50 B cells of anti-alpha(1,3) specificity must be present per animal to permit a measurable response. Surprisingly, the expression of a gene locus regulating lambda1 light chain expression (rlambda1 locus) shows a clear gene dosage effect with rlambda1lo/rlambda1 + heterozygotes having 1/2 the number of lambda1ASCs and 1/2 the amount of serum lambda1 Ig as rlambda1 +/rlambda1 + homozygotes. This fact permits an analysis of the relationship between germ-line v-genes and their individual expression in serum Ig. The rlambda1 locus controls specifically a DNA-level event which occurs in stem cells as they become committed to lambda1 light chain expression. We postulate that the rlambda1 locus represents one of the DNA level recognition sites involved in the translocation event which places the vlambda1 and clambda1 structural genes in a transcriptional unit.

Animals↗
PubMed1978

Divalent cation-dependent stereospecificity of adenosine 5'-O-(2-thiotriphosphate) in the hexokinase and pyruvate kinase reactions. The absolute stereochemistry of the diastereoisomers of adenosine 5'-O-(2-thiotriphosphate).

31P NMR studies with Cd(II) and Zn(II) chelates of adenosine 5'-O-(3-thiotriphosphate) (ATPgammaS) and the Cd(II) chelate of adenosine 5'-O-(2-thiotriphosphate) (ATPbetaS) indicate that these metal ions chelate to the sulfur atom of the thiophosphate group. Since Mg(II) chelates to oxygen of the thiophosphate group of diastereoisomer is equivalent to the configuration of the Cd(II) chelate of the opposite diastereoisomer. As a consequence, an inversion of the stereospecificity is observed when Cd(II) is substituted for Mg(II) in the phosphoryl transfer reactions catalyzed by yeast hexokinase and rabbit muscle pyruvate kinase. When Co(II) is the activating ion for yeast hexokinase with ATPbetaS as substrate, no stereospecificity is observed. Since the absolute configuration for the diastereoisomer of Co(III)(NH3)4ATP which is the active substrate for yeast hexokinase has been established by Cornelius and Cleland (Cornelius, R. D., and Cleland, W. W. (1978) Biochemistry, in press), the absolute stereochemistry of the Mg(II) complex of the B isomer of ATPbetaS is now established by its stereospecificity in the hexokinase reaction.

Adenosine Triphosphate↗
PubMed1978

Metal dependence of the phosphate (oxygen)-water exchange reaction of Escherichia coli alkaline phosphatase. Kinetics followed by 31P(18O) NMR.

Phosphate-water oxygen exchange catalyzed by Escherichia coli alkaline phosphatase was monitored using the 18O shift on the 31P NMR signal of inorganic phosphate. Different kinetic patterns were observed with native zinc enzyme and with its cobalt analogue. For native enzyme at pH values ranging from 4.4 to 10.0, the distribution of 18O species in Pi, viz. P18O4, P18O316O,P18O216O2,P18O16O3,P16O4, with time is compatible with a kinetic scheme in which E-P, the noncovalent enzyme-phosphate complex, dissociates more rapidly than it forms the covalent complex E-P. For the cobalt enzyme at pH 6.8, the distribution of 18O species in Pi with time is different and leads to the conclusion that formation of E-P is more rapid than dissociation of Pi from E-P-A computer simulation gave good quantitative agreement with the observed distribution for the time course of the cobalt enzyme reaction when the ratio of the rate of formation of E-P to dissection of E-P was assumed to be 3 +/- 0.5.

Alkaline Phosphatase↗