On tyrosinase ofDolichos lablab
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As a preliminary to a purification and study of the nature of the enzyme, methods for a quantitative estimation of tyrosinase have been standardised. The O2-uptake with mono- and di-hydroxy phenols has been studied in this connection. While the direct oxidation of phenol andp-cresol serves admirably as a measure of the enzyme, the oxidation of catechol fails to fulfil the conditions. To secure a steady rate of O2-uptake proportional to enzyme concentration, the direct oxidation of catechnol cannot be adopted but the oxidation of either ascorbic acid or hydroquinone (or ferricyanide) through the agency of catechol as “carrier”, fulfils the requirements. The formation of quinone bodies, the products of oxidation of various substrates by the enzyme, could be followed also iodimetrically.
The general substrate specificity of the enzyme suggests that it is not a “laccase” since the enzyme preparations have been found to be inert towardsp-dihydroxy compounds. The fact that the enzyme preparations oxidise several mono- and di-hydric phenols, necessitates a deeper study of the influence of further purifications on substrate specificity.
KeywordsCatechol Hydroquinone Enzyme Concentration Direct Oxidation Hexose Monophosphate
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