HYDROXYPYRUVATE REDUCTASE

Chloroplasts contain a specific glyoxylate reductase active with NADPH as coenzyme an enzyme in peroxisomes that catalyzes glyoxylate reduction by NADH is not specific and probably functions mainly as hydroxypyruvate reductase (Tolbert et al., 1970) (this is discussed in Section II,A,2). These enzymes could conceivably be involved in the oxidation of glycolate to provide glyoxylate for synthesis of glycine. 

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. 

A number of enzymic steps of the photorespiratory pathway, including the reduction of hydroxypyruvate to glycerate, are located in the peroxisomes (Fig. 2). For this reaction occurring at high rates the NADH has to be provided from outside the peroxisomes. Peroxisomal enzymes, such as hydroxypyruvate reductase, show latency (13). Recent experiments carried out in our laboratory have shown that this latency is not due to an impermeability of the peroxisomal membrane. It appears that the peroxisomal proteins form a dense matrix which is not affected by... 

For Method see (10,13). By using hydroxypyruvate reductase as marker enzyme, the activity obtained with the isolated peroxisomes was related to the chlorophyll content in a spinach leaf. 

Enzyme activities of nonreversible NADP-glyceraldehyde 3-phosphate dehydrogenase and NADP-isocitrate dehydrogenase as marker for the cytosol, hydroxypyruvate reductase for peroxisomes and cytochrom c reductase for mitochondria were 0.3 to 2% compared to those of the total leaf extract. 

This enzyme [EC 1.1.1.29], also known as hydroxypyru-vate reductase and hydroxypyruvate dehydrogenase, catalyzes the reaction of (R)-glycerate with NAD to produce hydroxypyruvate and NADH. 

Glyoxylate reductase [EC 1.1.1.26] catalyzes the reversible reaction of glycolate with NAD+ to produce glyoxylate and NADH. The enzyme will also catalyze the NADH-dependent interconversion of hydroxypyruvate to D-glycerate. Glyoxylate reductase (NADPH) [EC... 

Rumsby G, Cregeen DP Identification and expression of a cDNA for human hydroxypyruvate/glyoxylate reductase. Biochim Biophys Acta 1999 1446 383-388. 

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