Phenol oxidase activity and phenotypic expression of the melanotic tumor strain tug in Drosophila melanogaster.

INCE the report of BRIDGES (1916), various hereditary strains of melanotic tumor of Drosophila have been studied genetically, physiologically and biochemically (BURDETTE 1959; RIZKI 1960). The tumor strains are characterized by the appearance of melanized masses in the abdomen largely during the later stages of larval life. The melanized masses have commonly been called “melanotic tumors”, though they result from in situ outgrowths of proliferating cells (RIZKI 1960). Since the tumor is intimately related to melanin pigment and the melanin-forming system of Drosophila has been studied rather thoroughly in relation to body-color mutants ( OHNISHI 1954a, 1954b; LEWIS 1960; MITCHELL, WEBER and SCHAAR 1967), it seems justifiable to investigate the relationship between the phenotypic expression of the melanotic tumor and the melaninforming system. Phenol oxidase (0-diphenol: 0, oxidoreductase, EC 1.10.3.1 ., customarily called tyrosinase, dopa oxidase, phenolase and phenol oxidase) is considered to be responsible for the melanin formation. The enzyme occurs in the body fluids of Diptera as a pre-enzyme and is activated by a protein factor (OHNISHI 19531959; HOROWITZ and FLING 1955; MITCHELL and WEBER 1965). The enzyme activity varies during the course of development ( OHNISHI 1953; 1954b; GEIGER and MITCHELL 1966). For this reason, care must be taken to evaluate enzyme activity in a carefully selected developmental stage in which maximal activity of the enzyme is known to occur. Present study revealed that the activity of the phenol oxidase of the melanotic tumor strain tug is consistently lower than that of the isogenic wild strain. It was further shown that, if the comparison is made between the tumor-bearing individuals and the false-normal ones in the same line of the tumor strain, the reduced enzyme activity is correlated with the phenotypic expression of the melanotic tumor.