Affiliation:
1. Department of Microbiology and Immunology, McGill University, Montreal, Quebec, Canada
Abstract
Cryptococcus neoformans
produces brown pigmented colonies when grown on agar media made from an extract of potatoes and carrots, broad beans (
Vicia faba
), or
Guizotia abyssinica
seeds. Since other yeasts do not produce the pigment, these media are useful as differential isolation media for
C. neoformans
. Similar specific pigment was produced by
C. neoformans
on chemically defined agar media which contained six different substrates of phenoloxidase (
o
-diphenol: oxygen oxidoreductase EC 1.10.3.1) an enzyme which catalyses the oxidation of
o
-diphenols to melanin. Substrates were incorporated singly into the media and included L-3, 4-dihydroxyphenylalanine (L-DOPA), chlorogenic acid, protocatechuic acid, catechol, norepinephrine, and 3-hydroxytyramine hydrochloride (dopamine). No pigment was produced on media without substrate. Phenoloxidase activity in (NH
4
)
2
SO
4
precipitates of
C. neoformans
cell-free extract was assayed by measuring increases in absorbance at 480 nm produced in solutions of L-DOPA. This reaction showed oxygen uptake and was effectively inhibited by copper chelators, but not by catalase. The enzyme also oxidized the five other substrates which induced pigment formation. Electron micrographs of cells incubated in L-DOPA showed deposition of the pigment in the cell wall.
Publisher
American Society for Microbiology
Subject
General Pharmacology, Toxicology and Pharmaceutics,General Immunology and Microbiology,General Biochemistry, Genetics and Molecular Biology,General Medicine
Cited by
27 articles.
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