Kyoichi Kobashi

Catalytic oxidation of sulfhydryl groups by o-phenanthroline copper complex

Abstract 1. 1. Catalytic amounts of o -phenanthroline were found to enhance the rate of air-oxidation of all sulfhydryl groups tested in the presence of copper ions at neutral pH. This reaction was prevented by other metal ions which bind o -phenanthroline, as well as by reagents which chelate copper ions. 2. 2. For this reaction, molecular oxygen was essential, one-quarter mole of which was utilized per mole of sulfhydryl group oxidized. 3. 3. The most effective complex as a catalyst of the reaction was found to be ( o -phenanthroline) 2 -Cu 2+ complex. Cu + was detected in the reaction mixture under anaerobic conditions. 4. 4. The interpretation is discussed that o -phenanthroline necessarily acts as a metal chelator in the inhibitory action of this reagent on any enzyme.

Effect of acyl residues of hydroxamic acids on urease inhibition

Abstract 1. 1. As regards the relationship between carbon number of acyl- or p- alkoxybenzohydroxamic acids and their inhibitory powers on urease (urea amidohydrolase, EC 3.5.1.5) activity, heptylo- and caprylohydroxamic acids in the series of the former and p- methoxybenzohydroxamic acid in the series of the latter showed the maximum inhibitory power. An increase in the number of carbon atoms of the acyl- or alkoxymoieties led to a marked decrease in inhibitory power, which might be attributed to the decrease of their hydrophilic properties. 2. 2. Substitution with various groups at the meta - or para -position of benzohydroxamic acid did not affect the inhibitory power. Ortho -substituted derivatives, however, were markedly less inhibitory. These observations cannot be explained as being due to the effect of electronic polarization, but can be accounted for as being brought about by the “ortho effect”, in the sense that a steric hinderance was caused by ortho -substitution in the benzohydroxamic acid at the active site of urease. 3. 3. o- Aminobenzohydroxamic acid, a unique example among ortho -substituted derivatives, was found to be one of the most powerful inhibitors. Therefore a certain electronegatively charged group might possibly be located close to the active site of urease. However, methylation of the o- amino group of the compound reduced markedly its inhibitory power, this observation probably being attributable to the increase of steric size in the ortho -position. 4. 4. Among hydroxamic acids derived from pyridine carboxylic acid, the position of the hydroxamic acid moiety influenced significantly the inhibitory power on the urease activity. The α-amino group of hydroxamic acid derived from some α-amino acids did not affect the inhibitory power. 5. 5. Compared with various related compounds of hydroxamic acid and urea on their effect on urease activity, it is very probable that -CONHOH- is the group which is absolutely necessary in the chemical structure for the inhibition of urease activity. Both the properties of hydroxamic acids to form a coloured complex with Fe 3+ and their ionization constants had no correlation with their inhibitory powers on urease activity.

The limited proteolysis of rabbit muscle aldolase by cathepsin B1.

Abstract Rabbit muscle aldolase is inactivated by cathepsin B1 to approximately 10 percent of the original activity for fructose-1, 6-bisphosphate cleavage without change in the fructose-1-phosphate cleavage activity. Activity loss is related to release of one mole of the dipeptide, alanyl-tyrosine, per mole of the enzyme. The additional three moles of the peptide are released without further loss of the residual activity.