Oxidation of 3,4-dihydroxyphenylalanine by connective tissue constituents. Identification of Mycobacterium leprae not related to phenolase activity.

The oxidation of 3,4-dihydroxyphenylalanine (DOPA) was studied by spectrophotometric methods at pH 6.8. In the presence of L- or D-DOPA, a color development occurred in the presence of the following substances as measured by increase in absorption both at 540 nm and 480 nm: hyaluronic acid, trypsinized human skin and umbilical cord extract, trypsin treated rat tissue from subcutaneous rat leproma, trypsin treated M. lepraemurium isolated from rat lepromata, and trypsinized M. leprae isolated from non-treated lepromatous leprosy cases. Normal human skin and connective tissue extract and nontrypsinized connective tissue of rat leprosy granuloma did not oxidize DOPA. While the trypsin-treated partially purified M. leprae suspension oxidized DOPA at both wave-lengths, the hyaluronidase-treated same suspension of M. leprae failed to oxidize these phenolic compounds. Mushroom tyrosinase oxidized D-DOPA, L-DOPA, epinephrine and norepinephrine at 480 nm. Hyaluronic acid also oxidized epinephrine and norepinephrine at both wave-lengths. Since it is known that M. leprae in the human host is closely associated with the presence of the acid mucopolysaccharides of the skin, and since acid mucopolysaccharides and skin constituents strongly oxidized DOPA, and since the hyaluronidase treated M. leprae failed to oxidize DOPA, it became evident that hyaluronic acid and not M. leprae is responsible for DOPA oxidation, and phenolase activity is not associated with the metabolism of M. leprae. Evidence is presented that DOPA is not a unique characteristic of the human leprosy bacillus. For instance, trypsin-treated murine leprosy bacilli from the rat strongly oxidized DOPA. The reaction of DOPA oxidation, therefore, must be rejected as a test for the identification of M. leprae. The obtained results confirmed the pertinent findings of Skinsnes and his co-workers.