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Biomedical subjects

K S Venkatasubban

Publications and source records attributed to K S Venkatasubban.

2 recordsLinked to original sources

The proton inventory technique.

The proton inventory technique uses the dependence of enzymic reaction rate on the atom fraction of deuterium present in mixtures of protium oxide and deuterium oxide to deduce for simple cases the number of exchangeable hydrogenic sites that produce isotope effects, and the magnitude of the isotope effect generated at each site. For more complex cases, other information, such as the participation of more than a single step in limiting the rate, may be obtained. The background of the method, the conduct of the experiments and the interpretation of the results are briefly reviewed. The method is then illustrated in its application to various enzyme systems by a series of case histories.

Asparaginase↗

Carbon dioxide hydration activity of carbonic anhydrase in mixtures of water and deuterium oxide.

We have measured the hydration of CO2 catalyzed by bovine red cell carbonic anhydrase in mixtures of H2O and D2O at pH(D) which is in the plateau region of the pH--activity profile. The steady-state parameters for hydration Vmax and Km both show an exponential dependence on the atom fraction of deuterium in solvent water. These observed solvent isotope effects cannot be fit to a model involving one hydrogen but must arise from the contributions of two or more hydrogens which change their fractionation factor in the transition state of the rate-limiting step of the catalysis. On the basis of previous evidence, this step is taken to be an intramolecular proton transfer which our results suggest involves water bridges. The dependence of the rate constant for the uncatalyzed reaction between CO2 and water has a nonlinear dependence on the atom fraction of deuterium in the solvent. We conclude that the observed isotope effect must arise from more than one hydrogen in the transition state.

Animals↗