Abstract
Investigations were made of the inhibitory effects of hydroxamic acids on partially purified urease [EC 3. 5. 1. 5] extracted from Proteus vulgaris OX19 and on the ureolytic activity of the intact cell.
1. The inhibition was progressive with time and affected by reaction temperature. The inhibition by caprylohydroxamic acid on cell-free urease activity was not affected by cysteine. Caprylohydroxamic acid was found to be the most potent inhibitor showing an apparent I50 value of 8.0×10-7M for the cell-free enzyme and 6.0×10-6M for intact cell, although its effect on bacterial urease was considerably less than that on plant urease (I50=9.3×10-8M). The difference in the inhibitory effect of benzohydroxamic acid on the two enzymes was even more pronounced, with I50=2.5×10-5M for bacterial urease and I50=3.8×10-7M for plant urease. These results suggest that the active site of bacterial urease differs in its affinity to phenyl group from that of plant urease.
2. A rather broad optimal pH range (pH8.0-9.0) of inhibition was observed, which closely resembled that of the enzymatic activity. This resemblance suggests that hydroxamic acid combines with the active site of bacterial urease.
3. The increase of carbon number of n-aliphatic hydroxamic acid led to maximum inhibition at C8 derivative and then to a remarkable decrease in their inhibitory power. Among o-or p-substituents of benzohydroxamic acid with-CH3, -Cl, -NO2, -OH, -OCH3, and-OC4H9 p-substituted derivatives showed almost the same inhibitory powers as benzohydroxamic acid, whereas o-substituted derivatives were markedly less inhibitory towards both cell-free and intact cell systems. Among the pyridine derivatives tested, nicotinohydroxamic acid was the most potent inhibitor for both systems, which suggests that the position of basic group has a significant influence on the inhibitory power of hydroxamic acid derivatives.
