Tyrosinase Activity (TH, DO, PAGE‐Defined Isozymes) and Melanin Production in Regenerating Hairbulb Melanocytes of Lethal Yellow (Ay/a), Black (a/a), Agouti (AwJ/AwJ) and Albino (a/a/c2J/c2J) Mice (C57BL/6J)

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Abstract
We compared tyrosinase activity (TH, DO, and native PAGE‐defined isozymes) and melanin production in participate and soluble fractions of hairbulb melanocytes of lethal yellow (Ay/a C/C), nonagouti black (a/a C/C), and albino (a/a c2J/c2J) of 3‐, 6‐, 9‐, and 12‐day regenerating hairbulbs. With respect to tyrosine hydroxylase (TH) and dopa oxidase (DO) activities, Ay/a melanocytes possessed only 25‐35% of the activity of a/a; there were no genotype differences in either the subcellular distribution of activity in soluble and particulate fractions or in the relative increases of activity over the 12‐day developmental period. TH data on wild‐type agouti (AwJ/AwJ) mice over the 3‐11 day regeneration interval showed an activity intermediate between that of a/a and Ay/a; the rate of TH increase reflected black and yellow phases of the agouti hair cycle. Analyses of the number and densities of dopa‐sensitive bands following native PAGE of 3‐, 6‐, 9‐, and 12‐day hairbulb fractions of a/a and Ay/a mice suggested stage‐dependent patterns. A comparison of rates and amounts of melanin production in 3‐, 6‐, 9‐, and 12‐day fractions showed consistent melanin production in Ay/a to be 10‐20% that of a/a; however, fold increases in melanin production over the four stages were similar between genotypes. Overall, tyrosinase activity data support the notion that agouti locus modification of tyrosinase activity is a graded or quantitative rather than a qualitative phenomenon.