|Gibbs, R.G.; Morris J.G.
|Glycine-glyoxylate metabolism: β-hydroxyaspartate pathway (Micrococcus denitrificans)
|This chapter discusses glycine–glyoxylate metabolism. Three enzyme systems—namely, glyoxylate-L-aspartate aminotransferase, erythro-β-hydroxyaspartate aldolase, and erythro-β-hydroxyaspartate dehydratase––play an essential role in the growth of Micrococcus denitrificans on glycolate or on other precursors of glyoxylate. The very active glyoxylate-aspartate aminotransferase of Micrococcus denitrificans grown on glycolate or on other sources of glyoxylate is a key enzyme of the β-hydroxyaspartate pathway, wherein its role is to catalyze the synthesis of glycine from glyoxylate. Glyoxylate-dependent formation of oxaloacetate from L-aspartate is continuously assayed by following nicotinamide adenine dinucleotide phosphate (NADPH) oxidation at 340 mμ in the presence of an excess of the NADPH-linked malate dehydrogenase supplied by an extract of succinate-grown Micrococcus denitrificans. All purification operations are carried out at 0–4°. Erythro-DL-β-hydroxyaspartate is a competitive inhibitor of the enzyme, both when it is utilizing L-aspartate and when L-serine is the amino donor. Maleate, aminoacetonitrile, NH+ ions, and high concentrations of Tris-HCl buffer are also inhibitory. The pH optimum is about pH 7.