Serine hydroxypyruvate transaminase

Sallach observed the presence of a serine-hydroxypyruvate transaminase in liver and kidney of a number of mammalian species and partiaUy purified the enzyme from dog liver acetone powder. Alanine and pyruvate were specific for the transamination reaction, and transamination was shown to be reversible and to proceed in either direction by incubating serine with pyruvate or hydroxypyruvate with alanine. 

Hydroxypyruvate is primarily derived from serine through a transamination catalyzed by an alanine hydroxypyruvate transaminase. It is believed that excessive amounts of hydroxypyruvate are converted to l-glycerate (the reaction catalyzed by lactic dehydrogenase) because of a lack of D-glyceric dehydrogenase which catalyzes the conversion of hydroxypyruvate to D-glyceric acid. 

Many plant tissues contain hydroxypyruvate reductase (o-glycerate dehydrogenase) but it is especially active in leaves (Stafford et al., 1954 Stafford and Magaldi, 1954). Tolbert et al. (1970) purified the spinach enzyme and investigated its properties. It catalyzes reduction of hydroxypyruvate to D-glyceric acid by NADH [Eq. (3)]. Although the equilibrium is toward glyceric acid rather than hydroxypyruvate, the presence of sufficient amino donor and an appropriate transaminase would allow serine synthesis by the nonphosphorylated pathway with Eq. (3) as an intermediate step. 

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