C pigment locus mutants of the fowl produce enzymatically inactive tyrosinase‐like molecules

Three albino mutants of the fowl were tested for tyrosinase activity. Two of these mutants (c and c^a) are alleles at the autosomal C locus, while the third mutant (s^al) is sex‐linked. Both the standard type, E, and s^al are tyrosinase positive whereas the two C mutants are tyrosinase negative. Anti‐chicken tyrosinase mouse serum was produced and all four genotypes were found to have cross‐reacting material to this antiserum. Tyrosinase from the standard type was isolated and its location on denaturing two‐dimensional gels determined. A co‐migrating series of spots was found within the protein pattern of both the standard type and the tyrosinase positive albino, s^al. The same pattern of spots was also observed for c and c^a with no apparent change in either the pI or the molecular weight. Transmembrane blots also showed spots that reacted with anti‐tyrosinase serum in all four genotypes and that migrated to the same location as that of standard tyrosinase. It is proposed that both c and c^a are CRM⁺ mutants which produce tyrosinase‐like molecules that are inactive due to a change that is electrophoretically and antigenically “silent”.