Activation of Enzymes

More recent studies of the properties of arginase have stressed the probable significance of metal ion chemistry for the mechanism of its action (1).Previous reports (2,3) from this laboratory have dealt with the inhibition of activity of liver arginase by a variety of reagents and the restoration of activity by certain heavy metal ions (especially Co ff, Ni++, and Mnff), with the existence of an argininolytic enzyme in the jack bean which also is remarkably activated in the presence of certain of these ions, and with evidence pointing to a possible role of metal-coordinative processes in the enzymatic hydrolysis of d-arginine.From potentiometric titrations of d-arginine in the presence of heavy metal ions (3) it is clear that the a-amino group plays an important role in the formation of metallo complexes derived from this amino acid.In this respect arginine as compared with simpler amino acids (e.g., glycine) displays no essential peculiarity.This raises a question with reference to the necessity for the a-amino substituent in the substrate upon which the argininolytic enzymes act.Insufficient information upon this point has been afforded by the already extensive studies upon the specificity of arginase.* For related studies dealing with certain adjacent fields of biological catalysis and not included in the numbered series, see (1) and Am.J.