Tyrosinase exhibits lag at pH 6.8 under steady state concentrations of tyrosine and 3,4-dihydroxy phenyl alanine in melanoma tissue.
Tyrosine to dopa ratio determines the extent of lag in cresolase activity of tyrosinase when assayed at pH 6.8. The levels of tyrosine and dopa in B-16 murine melanoma tissue were found to be 213 and 13 mmoles/g fresh wt of tissue respectively. Cresolase activity of tyrosinase, when assayed at the above steady state levels of tyrosine and dopa at pH 6.8, exhibited a lag of 5-15 min depending on the amount of enzyme used in the assay mixture and the initial enzyme activity was zero. Under in vivo conditions, the enzyme with zero initial activity can not be active and therefore a far reaching conclusion is that tyrosine to dopa ratio may not regulate the enzyme activity, unlike under in vitro conditions. Possible modes of the regulation of tyrosinase under in vivo conditions are discussed.
Chintamaneni
C
C
Biochemistry Department, All India Institute of Medical Sciences, New Delhi.
Nadimpalli
A R
AR
Abburi
R
R
D000818:Animals; D004295:Dihydroxyphenylalanine; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008546:Melanoma, Experimental / Q000201:enzymology; D051379:Mice; D014442:Monophenol Monooxygenase / Q000378:metabolism*; D014443:Tyrosine
D014443:Tyrosine; D004295:Dihydroxyphenylalanine; D014442:Monophenol Monooxygenase