Abstract
1. 1. The effect of pH on V and K m for the action of purified d-amino acid oxidase ( d-amino acid: O 2 oxidoreductase (deaminating), EC 1.4.3.3) of pig kidney has been studied for four substrates. 2. 2. The pH curves with saturating substrate concentrations ( V against pH) may differ considerably from those obtained by the common practice of using fixed substrate concentrations, which are not sufficient to saturate the enzyme at all pH's ( v against pH). 3. 3. The four substrates give markedly different V-pH curves. 4. 4. The effects of pH on K m are very similar for d-alanine and d-methionine, showing two p K's of about 7.5 and 10 in the enzyme-substrate complex, one of 8.5 in the free enzyme, and one in the range 9.2–9.8 in the free substrate. The curve for glycine differs somewhat in form, and that for d-norvaline is completely different. 5. 5. The effects of pH on K i for an aliphatic and an aromatic acid which act as competitive inhibitors show a single p K of 8.5 in the free enzyme and none in the enzyme-inhibitor complex.
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