The oxidation of d- and l-glycerate by rat liver |
| |
Authors: | P. D. Dawkins and F. Dickens |
| |
Affiliation: | Courtauld Institute of Biochemistry, The Middlesex Hospital Medical School, London, W. 1 |
| |
Abstract: | 1. The interconversion of hydroxypyruvate and l-glycerate in the presence of NAD and rat-liver l-lactate dehydrogenase has been demonstrated. Michaelis constants for these substrates together with an equilibrium constant have been determined and compared with those for pyruvate and l-lactate. 2. The presence of d-glycerate dehydrogenase in rat liver has been confirmed and the enzyme has been purified 16–20-fold from the supernatant fraction of a homogenate, when it is free of l-lactate dehydrogenase, with a 23–29% recovery. The enzyme catalyses the interconversion of hydroxypyruvate and d-glycerate in the presence of either NAD or NADP with almost equal efficiency. d-Glycerate dehydrogenase also catalyses the reduction of glyoxylate, but is distinct from l-lactate dehydrogenase in that it fails to act on pyruvate, d-lactate or l-lactate. The enzyme is strongly dependent on free thiol groups, as shown by inhibition with p-chloromercuribenzoate, and in the presence of sodium chloride the reduction of hydroxypyruvate is activated. Michaelis constants for these substrates of d-glycerate dehydrogenase and an equilibrium constant for the NAD-catalysed reaction have been calculated. 3. An explanation for the lowered Vmax. with d-glycerate as compared with dl-glycerate for the rabbit-kidney d-α-hydroxy acid dehydrogenase has been proposed. |
| |
Keywords: | |
|
|