Abstract
Some properties of α-keto acid carboxylases in plant extracts were studied. Phenol (2 mg./ml.) inhibited carboxylase but did not interfere with the activity of glutamic acid decarboxylase. This specific effect of phenol permitted the use of squash preparations for the quantitative determination of glutamic acid in the presence of pyruvic acid. The inhibition of carboxylase by 23 compounds related to phenol was measured. It was observed that many plant extracts contained in addition to glutamic acid decarboxylase and α-carboxylase an enzyme mechanism which liberated 2–3 moles of CO 2 with ketoglutaric acid as substrate. Optimal activity of this degradation occurred at pH 6.0. The effect of plant extracts on ketoglutaric acid was abolished rapidly by dialysis, and was restored on addition of concentrated dialyzate. The substances responsible for the reactivation of dialyzed extracts were identified as l-aspartic acid and l-alanine. It was found that the first step in the reaction of plant extracts with ketoglutaric acid was a transamination process leading to the formation of glutamic acid and oxalacetic acid or pyruvic acid, depending on the amino group donor.
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