The Activation of Arginase

The mechanism of arginase activation has been widely studied during the past few years. Salaskin and Solowjew (1) and Waldschmidt-Leitz, Schaffner, and Kocholaty (2) believed that sulfhydryl compounds were the specific activators of arginase. This viewpoint was attacked by Edlbacher, Kraus, and Walter (3), and by Klein and Ziese (4), who presented evidence that the effect obtained with sulfhydryl varied with the pH and with the purity of the enzyme preparation. Later, Salaskin and Solowjew (5), and Waldschmidt-Leitz, Scharikova, and Schaffner (6), reached the conclusion that sulfhydryl compounds in combination with heavy metal (Fe” or Cu’) act as the true specific activators of the enzyme. Recent experiments of Purr and Weil (7) have demonstrated that sulfhydryl compounds cannot be considered to be specific activators, since other intermediary metabolic products (e.g. alloxan-Fe”, ascorbic acid-Fe”, and methylglyoxalFe”) in combination with iron are also able to actiyate arginase. Results obtained by Klein and Ziese (8) point t,o a similar conclusion. The dependence of arginase activation on oxidation-reduction processes was investigated by Waldschmidt-Leitz and Kocholaty (9), who maintained that oxygen is necessary for activation. Klein and Ziese (8) found that oxidizing agents had an activating effect only in the case of purified arginase, and that the process was one of simple oxidation and not dependent on the establishment of a definite oxidation-reduction potential. Edlbacher, Kraus, and Leuthardt (10) on the other hand consider oxygen as an inhibitor of the enzyme, the cysteine-Fe” complex merely acting as a protector against oxygen. In a later paper Leuthardt