Biomedical subjects
A A Bell
Publications and source records attributed to A A Bell.
Melanins and their importance in pathogenic fungi.
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Histamine release from mast cells by terpenoid aldehydes isolated from glanded varieties of cotton.
In vivo and in vitro experiments have strongly indicated that mast cell degranulation, with its release of histamine and other pharmacoactive compounds, plays a major role in the acute respiratory response of humans following inhalation of cotton textile dust. Thirteen terpenoid aldehydes isolated from the glands of the two major Gossypium species used for cotton production, stimulated significant release of histamine from mast cells at concentrations of 1 micrograms/mL. Eleven of the thirteen compounds produce significant mast cell degranulation at concentrations well below the levels of free terpenoid aldehydes that could be expected to enter the lungs during an eight hour work day under the current permissible card room standards of 200 micrograms per cubic meter. Daily mast cell degranulation, stimulated by these terpenoid aldehydes could account for many of the pathophysiological changes found in the chronic byssinotic.
Ultrastructural and chemical distinction of melanins formed by Verticillium dahliae from (+)-scytalone, 1,8-dihydroxynaphthalene, catechol, and L-3,4-dihydroxyphenylalanine.
Microsclerotia of three melanin-deficient mutants of Verticillium dahliae formed malanin from (+)-scytalone, 1,8-dihydroxynaphthalene, catechol, and L-3,4-dihydroxyphenylalanine. The melanins formed from (+)-scytalone or 1,8-dihydroxynaphthalene resembled wild-type melanin chemically and ultrastructurally, whereas the melanins formed from catechol and L-3,4-dihydroxyphenlalanine were different. This suggests that scytalone and 1,8-dihydroxynaphthalene but no catechol or L-3,4-dihydroxyphenylalanine are natural intermediates of melanin biosynthesis in V. dahliae.
Pentaketide metabolites of Verticillium dahliae. 3. Identification of (-)-3,4-dihydro-3,8-dihydroxy-1(2h)-naphtalenone((-)-vermelone) as a precursor to melanin.
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Use of mutants to establish (+)-scytalone as an intermediate in melanin biosynthesis by Verticillium dahliae.
Melanin biosynthesis in Verticillium dahliae Kleb, was studied with mutants deficient for normal black melanin or for production of microsclerotia. Seven genetically different mutants had apparent blocks in melanin biosynthesis. Four mutants (brm-1 to -4) produced brown microsclerotia and extruded pigments into media; three (alm-1 to -3) produced albino microsclerotia. Other mutants produced no microsclerotia (nms) or had greatly reduced numbers of microsclerotia (rms). Mutation alm-1 was due to a single recessive gene; the other melanin-deficient characters were recessive but their genetic bases were not determined. Cultures of the brown mutants brm-1 and -3 extruded and accumulated a metabolite that blackened the albino microslerotia of alm-1 to -3. The metabolite was identified as (+)-scytalone (3,4-dihydro-3,6,8-trihydroxy-1(2H)naphthalenone). Pigment formed by alm-1 microsclerotia from (+)-scytalone had chemical and physical properties identical with those of melanin in the wild-type fungus. (+)-Scytalone was produced and converted to melanin by microsclerotia but not by conidia or hyphae. Conversion of (+)-scytalone to melanin appeared to involve two or more enzymes and probably involved conversions to 1,3,8,-trihydroxynaphthalene and 1,8-dihydroxynaphthalene. Albino mutants of Thielaviopsis basicola, Drechslera sorokiniana, Pleospora infectoria (Alternaria), Ulocladium sp., and Curvularia sp. also converted scytalone to pigments indistinguishable from the melanins found in their respective wild types. Scytalone melanin may be common in fungi with dark brown or black pigments.
Pentaketide metabolites of Verticillium dahliae. II. Accumulation of naphthol derivatives by the aberrant-melanin mutant BRM-2.
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