Enzymatic Studies of the Physiological Genetics of Guinea Pig Coat Coloration. I. Oxygen Consumption Studies.

HE GENETICS of coat color pigmentation in the guinea pig have been exT tensively analyzed by WRIGHT (1916, 1917, 1925, 1927). These studies have been supplemented by various attempts to discover the underlying inherited physio . logical processes, either by quantitative determinations of pigmented end product (E. S. RUSSELL 1939; HEIDENTHAL 1940; WRIGHT and BRADDOCK 1949; WRIGHT 1949) or by assays for enzyme (dopa oxidase) activity in the skins of a wide variety of genotypes (W. L. RUSSELL 1939; GINSBURG 1944). A detailed consideration of these different types of studies is contained in WRIGHT’S review (1942). The study reported here represents an additional attempt to ascertain inherited melanin-forming enzyme variations in guinea pig skin, and some of these results have already been summarized (FOSTER 1952b). W. L. RUSSELL’S histochemical studies with incubated frozen skin sections involved visual grading of degree of blackening both in hair bulb and in basal epidermal melanocytes. His assays for dopa oxidase activity indicated a strong correlation between the intensity of the hair bulb reaction (but not that of the basal epidermal melanocytes) and the amount of natural yellow pigment (phaeomelanin) controlled by the genotype. A similar correlation was reported by GINSBURG, who performed turbidimetric assays for dopa oxidase activity in fresh and stored (“delayed”) skin extracts (1944). Our own results, while in many respects confirming thoseof RUSSELL and GINSBURG, tend on the whole, but with important exceptions, to indicate a correlation between genetically controlled amount of dark pigment (eumelanin) and tyrosinase or dopa oxidase activity. However, as will be discussed later, a t least some of the major apparent discrepancies between reported results can be reconciled on the basis of differing materials and methods.