Inability to demonstrate hydroxylation of tyrosine by murine melanoma "tyrosinase" (L-DOPA oxidase), using the tritiated water assay technique.

Validity of the tritiated water assay technique for tyrosine hydroxylase activity as a qualitative method was demonstrated with mushroom tyrosinase. Using this method, isolated murine melanoma "tyrosinase" (L-dopa oxidase) showed no tyrosine hydroxylase activity. This finding supports previous studies in our laboratory which used a variety of histochemical and biochemical methods.

Osmium zinc iodide reactive sites in the epidermal Langerhans cell.

Fixation of epidermis with a mixture of osmium tetroxide and zinc iodide (OsO(4)-ZnI(2)) for 24 hr renders the central periodic lamella of the Langerhans cell granule (LCG), the Golgi region, and the nuclear envelope of epidermal Langerhans cells preferentially visible. The use of this technique on Langerhans cells in normal epidermis and in epidermis of patients with histiocytosis (Letterer-Siwe disease) allows a broader visualization of the LCG's than was heretofore possible with routine glutaraldehyde-osmium tetroxide fixation and uranyl acetate-lead staining. The identical staining of Golgi apparatus and LCG favors the view that there is close relation between the Golgi area and the LCG's.

Tyrosinase inhibition: its role in suntanning and in albinism.

Tyrosinase inhibitor (molecular weight less than 5000; extracted from various melanomas) fully inhibits soluble tyrosinase but only partially inhibits tyrosinase "aggregated" into melanosomes; the inhibitor can be inactivated by ultraviolet light. S91 Albinotyrosinase Type B apparently cannot "aggregate" into melanosomes because its protein carrier is genetically altered. Therefore, albinotyrosinase remains vulnerable to its inhibitor and cannot produce melanin, even though the enzyme has a functioning active center.