Inhibition of soybean urease by polycarbonyl compounds

Competitive inhibition of soybean urease was studied at 36°C in aqueous solution (pH 4.95) in the presence of polycarbonyl compounds (PCCs): oxalyldihydrazide (ODH), its polydisulfide (poly(DSODH)), three cyclic β-triketones (CTKs), and seven cyclic PCC species of differing structure. The inhibition constants of ureolysis (K i ) varied in the range 8.5–3800 µM depending on the structure of organic chelators for the nickel atom in urease. It was shown that pH variation within the range from 3.85 to 7.40 exerted a strong effect on the values of K i of three CTKs and hydroxyurea, which was used as a reference: pH dependences of log K i were linear in all cases and displayed a break at pH 6.0–6.5. The most effective inhibitor of ureolysis was poly(DSODH), which contained ∼28 carbonyl groups in the polymer molecule. The role of such factors as the number of carbonyl groups per PCC molecule, mutual arrangement, and reaction medium pH in the efficiency of the process of urease inhibition is discussed.