乙胺硫脲抑制蘑菇酪氨酸酶活性动力学

Inhibitory kinetics of aminoethylisothiourea on mushroom tyrosinase activity

研究了乙胺硫脲对蘑菇酪氨酸酶单酚酶和二酚酶活性的抑制效应。结果表明,乙胺硫脲对酪氨酸酶单酚酶和二酚酶活性均有抑制作用,导致单酚酶活力和二酚酶活力下降50%的乙胺硫脲浓度(IC50)分别为14.8和45.2μmol/L。在降低酪氨酸酶酶活的同时,乙胺硫脲能明显延长单酚酶和二酚酶的延滞时间。探讨了二酚酶延滞时间产生的原因:乙胺硫脲与酪氨酸酶催化氧化产物多巴醌反应,形成了无色的L-DOPA衍生物,从而阻断了多巴色素的形成。乙胺硫脲对二酚酶的抑制作用表现为不可逆的竞争性抑制。并且,在反应体系中存在的铜离子仅能够部分的阻止乙胺硫脲对酪氨酸酶的抑制。

The inhibitory effects of aminoethylisothiourea(AET) on the monophenolase and diphenolase activities of tyrosinase were studied.It was found that aminoethylisothiourea could inhibit both the monophenolase and diphenolase activities of mushroom tyrosinase.The aminoethylisothiourea concentrations leading to 50% activity loss(IC50) were 14.8 μmol/L for monophenolase and 45.2 μmol/L for diphenolase,respectively.Increasing aminoethylisothiourea concentration provoked longer lag periods of monophenolase and diphenolaseas.It is concluded in diphenolase investigation that the lag period corresponded to the time in which aminoethylisothiourea was reacting on the enzymatically generated o-quinone.This study demonstrates that aminoethylisothiourea is an irreversible competitive inhibitor of the diphenolase activity of mushroom tyrosinase.Furthermore,the presence of copper ions in the reaction medium only partially prevented but could not revert the inhibition of aminoethylisothiourea on monophenolase and diphenolase activities of tyrosinase.