Phenol oxidase characteristics in mutants of Drosophila melanogaster.

INCE the very early experiments of GRAUBARD (1933), numerous investigators have examined the problem of genetic control of phenol oxidases in Drosophila with attention focused primarily on pigment production and thus on the color mutants. However, it has become clear that the function of such enzymes in cuticle formation is far more vital than in pigment production. It follows that if the same enzymes are involved in both processes, and this now seems highly probable, then mutations to enzyme loss would be lethal and mutations to pigment alterations must be due to modest alterations of structural proteins or entirely due to regulation of function. At present the latter interpretation appears the more attractive, particularly in view of the probability that the phenol oxidases play a dual role, having catalytic function in oxidation and also a function as material providing fixed macromolecular structure. Early evidence that can be interpreted in this direction ( HOROWITZ and FLING 1955) demonstrated that Drosophila extracts contain no phenol oxidase function prior to an incubation period to permit activation, and that after activation the product with enzyme function is easily sedimented by centrifugation. More recently (MITCHELL and WEBER 1965) it has been shown that at least five proteins are involved in the processes of phenol oxidase activation, and orderly aggregation of several different protein subunits to yield very large and complex structures has appeared as the best interpretation of the data. This postulation now receives further support from the data presented here on the macromolecular nature of the phenol oxidases produced in extracts of the Oregon-R wild strain of Drosophila melanogaster and in extracts of four pigmentation mutants. Based on velocity and equilibrium sedimentation studies in sucrose gradients, in vitro, activation to produce phenol oxidase activity yields at least seven active components relatively low in density but very large in size. Extreme and significant differences exist among the mutants and wild type.