The rate of formation of the stable red complex between cobalt, glycylglycine (GG) and molecular oxygen has been investigated over the range of pH 7 to 12.5. It appears that the formation of this complex requires as an intermediate a complex containing two hydroxyl ions, [(OH)(GG)2Co-C>2-Co(GG)a(OH)]~. Below pH 8 this intermediate is highly unstable and its presence can be deduced only from the pronounced />H-dependence of the reaction rate. At higher pH values the intermediate becomes increasingly stable and can be observed by its intense brown color. The important step in the forma-

Ribonuclease and carboxypeptidase are inactivated by ultraviolet light (2537 A.) with quantum yields of 0.03 and 0.001–0.005 respectively. The quantum yields for low molecular weight proteins are of the order of 0.03 and are higher than those for splitting peptide bonds in typical peptides (0.004–0.0004 or less). It is postulated that the primary process of inactivation involves modification of aromatic residues in proteins. A possible reason for the inverse relationship between quantum yields and molecular weights of enzymes and proteins is discussed.