Activation of a latent mushroom (Agaricus bisporus) tyrosinase isoform by sodium dodecyl sulfate (SDS). Kinetic properties of the SDS-activated isoform.
This study reports the activation of a latent mushroom tyrosinase isoform by sodium dodecyl sulfate (SDS). The activation process of latent mushroom tyrosinase by SDS is characterized by the presence of a lag period (tau) prior to the attainment of a steady-state rate (V(ss)). This could be related to a slow conformational change of the latent enzyme to render the active isoform. The molecular size of the latent isoform was 67 kDa as determined by SDS-PAGE and western-blotting assays. This size did not change after activation by SDS. The molecular size of the protease-activated isoform was 43 kDa. tau and V(ss) displayed a sigmoidal relationship to the concentration of SDS, but tau was not dependent on o-diphenol or enzyme concentration. Increasing SDS concentrations decreased tau, but then lower V(ss) values were detected because of a possible excess of unfolding and subsequent denaturation of the protein. The same reaction mechanism operated in both SDS-activated and protease-activated tyrosinase isoforms despite their different kinetic features. A possible mechanism for the activation of this latent tyrosinase by SDS is proposed.
Espín
J C
JC
Agrotechnological Research Institute (ATO-DLO), Bornsesteeg 59, P.O. Box 17, 6700 Wageningen, The Netherlands. J.C.ESPIN@ato.dlo.nl
Wichers
H J
HJ
D000363:Agaricales / Q000201:enzymology*; D000364:Agaricus / Q000201:enzymology*; D004789:Enzyme Activation; D007527:Isoenzymes / Q000378:metabolism; D007700:Kinetics; D014442:Monophenol Monooxygenase / Q000378:metabolism*; D012967:Sodium Dodecyl Sulfate / Q000494:pharmacology*
D007527:Isoenzymes; D012967:Sodium Dodecyl Sulfate; D014442:Monophenol Monooxygenase