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The enthalpimetric determination of inhibition constants for the inhibition of urease by acetohydroxamic acid

100%

Zaborska W., Leszko M., Kot M., Juszkiewicz A.

Acta Biochimica Polonica

1997

tom 44

nr 1

The effect of concentration of acetohydroxamic acid (AHA) on inhibition of jack bean urease in phosphate buffer, pH 7.0, at 25°C, was studied. The measurements were performed at urease concentration of 2.5 mg/100 cm3 for concentrations of urea and AHA ranging in the range of 2-50 mmol dm-3 and 0.25-10 mmol dm-3, respectively. The reactions were monitored by two techniques: analytical and enthalpimetric. For the analytical technique the growth of ammonia concentration in the course of the reaction was determined. From the recorded progress curves the following parameters were calculated for each inhibitor concentration: the initial reaction rate, the steady-state rate and the inversion constant. From these parameters the inhibition constants of the initial and steady-state stages of the reaction, K\ and K\y were calculated. The former constant did not change whereas the latter one proved to decrease quickly with an increase in inhibitor concentration. This behaviour resulted from the fact that the inactive complex EI* was not a product of internal inversion but was formed in the reaction: — 2/3I + EI —> (EI • — 2/3I)*. The disso3ciation constant of this complex is equal to about 0.3 x 10-3 (mol dm-3)2/3.

The role of alkyl chain length in the inhibitory effect n-alkyl xanthates on mushroom tyrosinase activities

72%

Saboury A. A., Alijanianzadeh M., Mansoori-Torshizi H.

Acta Biochimica Polonica

2007

tom 54

nr 1

Sodium salts of four n-alkyl xanthate compounds, C2H5OCS2Na (I), C3H7OCS2Na (II), C4H9OCS2Na (III), and C6H13OCS2Na (IV) were synthesized and examined for inhibition of both cresolase and catecholase activities of mushroom tyrosinase (MT) in 10 mM sodium phosphate buffer, pH 6.8, at 293 K using UV spectrophotemetry. 4-[(4-methylbenzo)azo]-1,2-benzendiol (MeBACat) and 4-[(4-methylphenyl)azo]-phenol (MePAPh) were used as synthetic substrates for the enzyme for catecholase and cresolase reactions, respectively. Lineweaver-Burk plots showed different patterns of mixed, competitive or uncompetitive inhibition for the four xanthates. For the cresolase activity, I and II showed uncompetitive inhibition but III and IV showed competitive inhibition pattern. For the catecholase activity, I and II showed mixed inhibition but III and IV showed competitive inhibition. The synthesized compounds can be classified as potent inhibitors of MT due to their Ki values of 13.8, 11, 8 and 5 μM for the cresolase activity, and 1.4, 5, 13 and 25 μM for the catecholase activity for I, II, III and IV, respectively. For the catecholase activity both substrate and inhibitor can be bound to the enzyme with negative cooperativity between the binding sites (α > 1) and this negative cooperativity increases with increasing length of the aliphatic tail of these compounds. The length of the hydrophobic tail of the xanthates has a stronger effect on the Ki values for catecholase inhibition than for cresolase inhibition. Increasing the length of the hydrophobic tail leads to a decrease of the Ki values for cresolase inhibition and an increase of the Ki values for catecholase inhibition.

Ograniczanie wyników

2 Acta Biochimica Polonica

1 Alijanianzadeh M.

1 Juszkiewicz A.

1 Kot M.

1 Leszko M.

1 Mansoori-Torshizi H.

1 Saboury A. A.

1 Zaborska W.

1 2007

1 1997

Wyniki wyszukiwania

The enthalpimetric determination of inhibition constants for the inhibition of urease by acetohydroxamic acid

The role of alkyl chain length in the inhibitory effect n-alkyl xanthates on mushroom tyrosinase activities