On the possibility of involvement of glutamate glyoxylate and serine glyoxylate aminotransferases from rye [Secale cereale] seedlings in the metabolism of tetrapyrrole compounds

The activity of highly purified L-serine:glyoxylate aminotransferase (SGAT, EC 2.6.1 AS) from rye seedlings was inhibited competitively by 5-aminolevulinate (ALA, Ki = 5 mM) SGAT was activated by hematin. Protoporphyrin IX and hematin inhibited irreversibly the activity of highly purified glutamate:glyoxylate aminotransferase (GGAT, EC 2.6.1.2) from rye seedlings. SGAT was found to catalyse transamination between ALA and hydroxypyruvate, whereas GGAT that between ALA and 2-oxoglu- tarate or pyruvate. It is suggested that SGAT is involved in the process of degradation of the excess ALA which has not been incorporated into porphyrin compounds.