Co-Authors:
Kahn, V., Department of Food Science, Agricultural Research Organization, The Volcani Center, P.O. Box 6, Bet Dagan, 50250, Israel
Andrawis, A., Department of Food Science, Agricultural Research Organization, The Volcani Center, P.O. Box 6, Bet Dagan, 50250, Israel
Abstract:
Mushroom tyrosinase is affected by hydroxylamine (NH2OH) in several ways. At relatively low concentrations (up to 33 mM) NH2OH shortens the lag period of tyrosine hydroxylation. The o-dihydroxyphenolase activity of mushroom tyrosinase is slightly stimulated by short exposure to relatively low concentrations ofNH2OH (1.5 mM). Relatively high concentrations ofNH2OH (above 20 mM) inhibit the o-dihydroxyphenolase activity of the enzyme and lowers the extent of final pigment production. Preincubation of mushroom tyrosinase with different concentrations ofNH2OH for different times results in the inactivation of the enzyme. The rate of inactivation occurred much faster under anaerobic than under aerobic conditions. It was also found that NH2OH changes the spectra of o-quinones prepared chemically or of products formed during the oxidation of o-dihydroxyphenols by mushroom tyrosinase. These spectral changes were attributed to the formation of oximes (mono- or dioximes) as a result of an interaction between o-quinones and NH2OH. The apparent inhibition exerted by NH2OH on the o-dihydroxyphenolase activity of mushroom tyrosinase is, in part, due to spectral changes in pigmented product formation and, in part, due to the inactivation of the enzyme by NH2OH. © 1986.
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