Enzymically Active and Inactive Melanocyte Populations and Ultraviolet Irradiation: Combined Dopa-Premelanin Reaction and Electron Microscopy

Abstract

INTRODUCTION The electron microscopic ammoniated silver nitrate reaction for premelanin (1) has been shown to be specific for the cytoplasmic structure of the premelanosome itself in contrast to the dopa reaction which reveals tyrosinase activity. By demonstrating both the presence of the melanosome system and tyrosinase activity, the combined dopa-premelanin reaction (2) has been found to reveal not only active melanocytes (melanosome and tyrosinase synthesizing) but also the enzymically inactive or hypoactive melanocytes (melanosome synthesizing). Furthermore, it has been shown that the formation of premelanosomes is independent of tyrosinase synthesis and of the deposition of melanin, although these processes are normally coordinated in the cytoplasm of the melanocyte (3). An example of structurally normal premelanosome formation without melanin synthesis is seen in the melanocyte of the complete human and fish albino (4). It has also been found that the electron microscopic ammoniated silver nitrate reaction for premelanin can selectively reveal even these unmelanized premelanosomes (5). However, the recognition of melanocytes by the premelanin reaction at the light microscopic level requires the presence of a certain minimal number of premelanosomes regardless of the presence of tyrosinase activity, while the recognition of melanocytes by the dopa reaction requires the presence of a certain essential amount of tyrosinase activity regardless of the presence of premelanosome synthesis. It has been shown that non-melanosomal, cytoplasmic tyrosinase exists in pigment cells General Hospital, Detroit, and Veterans Administration Hospital, Dearborn, Michigan, U.S.A.