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- Title
Kinetic Evaluation of Aminoethylisothiourea on Mushroom Tyrosinase Activity.
- Authors
Shu-Bai Li; Hua-Li Nie; Hai-Tao Zhang; Yong Xue; Li-Min Zhu
- Abstract
This study demonstrates that aminoethylisothiourea (AET), a potent inhibitor of inducible nitric oxide synthase, is an irreversible competitive inhibitor of mushroom tyrosinase by chelation to the active site of tyrosinase when l-3,4-dihydroxyphenylalanine was assayed spectrophotometrically. The spectrophotometric recordings of the inhibition of tyrosinase by AET were characterized by the presence of a lag period prior to the attainment of an inhibited steady-state rate. The lag period corresponded to the time in which AET was reacting with the enzymatically generated o-quinone. Increasing AET concentrations provoked longer lag periods as well as a concomitant decrease in the tyrosinase activity. Both lag period and steady-state rate were dependent on AET, substrate, and tyrosinase concentrations. The inhibition of diphenolase activity of tyrosinase by AET showed positive kinetic cooperativity which arose from the protection of both substrate and o-quinone against inhibition by AET. The UV-visible spectrum of a mixture of tyrosinase and AET exhibited a characteristic shoulder peak ascribed to the chelation of AET to the active site of tyrosinase. Moreover, the presence of copper ions only partially prevented but not reverted mushroom tyrosinase inhibition when CuSO4 was added to the assay medium on tyrosinase activity.
- Subjects
THIOUREA; PHENOL oxidase; COPPER; CHELATION therapy; NITRIC oxide
- Publication
Applied Biochemistry & Biotechnology, 2010, Vol 162, Issue 3, p641
- ISSN
0273-2289
- Publication type
Academic Journal
- DOI
10.1007/s12010-009-8760-3