From Big Medical Encyclopedia

DOFA-REAKTSIYA — a method of identification of melanoblasts — the cells producing the melanin and its colourless prestages consisting in processing of fabrics solution L - 3,4-dioksifenil alanines (Dioxyphenilalanin). Reaction received the reduced designation DOPA (DOFA in the Russian pronunciation) on initial letters of the composed words. The method is offered in 1917 by B. Bloch.

Biochemical, the essence of a method consists that enzyme tyrosinase (see), contained in melanosoma and premelanosoma, translates tyrosine (see) in dioxyphenylalanine (see), and the last — in melanin (see). Positive D. - rubles give only melanoblasts, and in melanophores, cells which absorbed a pigment, reaction is always negative. There are many modifications of a method for a research of the frozen and paraffin sections using an autoradiography and a submicroscopy. The reaction demanding an incubation of the cells containing a tyrosinase in solution with dioxyphenylalanine in practice not always was successful, its results were often insufficiently reliable. Sensitivity and its reliability considerably increased using in the fixing solutions of 0,1 M of the kakodilatny buffer from pH 7,4 promoting preservation of tirozinazny activity; on this buffer 4% solution of formaldehyde or 2% solution of glutaraldehyde prepare. The main DOFA-solution, in Krom pieces of the studied fabric are incubated, consists of two parts mixed in equal proportions just before the use. Solution A: 0,2 M water solution of pH 7,4 sodium cacodylate; for its preparation dissolve 42,8 g of a reactant and 9,6 ml 1 N of HCl in 500 ml of a distilled water, and then bring the volume of solution to 1000 ml. Solution B: 0,2% DOFA solution in a distilled water. Both solutions store before the use separately at t ° 4 ° within several months.

Reaction is carried out as follows: fabric is cut in the cryostat; the cuts placed on glass are fixed at the room temperature within 1 hour in 4% solution of formaldehyde or in 2% solution of glutaraldehyde, then washed out in buffer solution of sodium cacodylate and incubated at t ° 37 ° during 4 — 7 hours in DOFA solution. At paraffin embedding pieces of fabric 0,1 — 0,2 cm thick are fixed in the same fixers, processed by DOFA-solution, in addition fixed in 10% neutral formalin and filled in in paraffin; gistol, drugs prepare usually. The offered technique allows to make a research of the frozen and paraffin sections in light, and also in a supermicroscope. At microscopy cytoplasm of melanoblasts diffuzno or is granulyarno painted in brown-black color.

- the river is applied to detection of melanoblasts for the purpose of diagnosis of pigment-free birthmarks and melanomas in biopsy and section material.

Bibliography: Gayer. An electronic histochemistry, the lane with it., page 84, etc., M., 1974; Pearce E. A histochemistry, theoretical and applied, the lane with English, page 464, M., 1962; P about m of e y with B. Mikroskopicheskaya of the technician" the lane with it., page 281, M., 1953; Voorhess M. L. Urinary excretion of DOPA and metabolites by patients with melanoma, Cancer, v. 26, p. 146, 1970, bibliogr.

A. M. Vikhert.