OXYMETRIC AND SPECTROPHOTOMETRIC STUDY OF THE ASCORBATE OXIDASE ACTIVITY SHOWN BY FROG EPIDERMIS TYROSINASE

Citation
Jr. Ros et al., OXYMETRIC AND SPECTROPHOTOMETRIC STUDY OF THE ASCORBATE OXIDASE ACTIVITY SHOWN BY FROG EPIDERMIS TYROSINASE, International journal of biochemistry & cell biology, 28(8), 1996, pp. 917-923
Citations number
35
Categorie Soggetti
Biology,"Cell Biology
ISSN journal
13572725
Volume
28
Issue
8
Year of publication
1996
Pages
917 - 923
Database
ISI
SICI code
1357-2725(1996)28:8<917:OASSOT>2.0.ZU;2-2
Abstract
Many studies concerning the effect of ascorbic acid on the action of t yrosinase on several substrates have been carried out with contradicto ry results. The results shown in this work comprise a hypothetical rea ction mechanism, which explains the ascorbate oxidase activity of frog epidermis tyrosinase. The reaction between frog epidermis tyrosinase and L-ascorbic acid was studied by oxymetric and spectrophotometric as says. The activity was linearly related to enzyme concentration, with a Michaelis constant for L-ascorbic acid of 0.160 +/- 0.009 mM and V-m ax of 90 +/- 4 nM/s. Maximum activity was obtained at pH 7.5. The stoi chiometry of the reaction was calculated by measuring the substrate (O -2 and L-ascorbic acid) consumption as web as the initial rates of the consumption of oxygen and the disappearance of L-ascorbic acid. The s toichiometry was found to be 1:2 (O-2:L-ascorbic acid). The action of the tyrosinase inhibitor tropolone was also studied. All the results p resent evidence concerning the ascorbate oxidase activity of frog epid ermis tyrosinase and a possible reaction mechanism based on the differ ent enzymatic forms of tyrosinase to explain such activity. Copyright (C) 1996 Elsevier Science Ltd