Enzymatic conversion of sterigmatocystin to aflatoxin B1.
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Date
1984
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Abstract
The age of Aspergillus parasiticus (1-11-105Wh1)
mycelium was found to have an influence on the level of enzymes,
responsible for the conversion of sterigmatocystin to aflatoxin
B[1] and O-methylsterigmatocystin, present. These enzymes were
active over a wide range of temperature and pH.
Production of a cell free system by lyophiliization
yielded the highest aflatoxin B[1] synthesising activity. Three
other methods of preparing the cell free system capable of
synthesising aflatoxin B[1] were also studied, ie,: french
press, protoplast, and grinding, but with limited success. The
lyophilized preparation had narrower temperature and pH optima
for the conversion than whole mycelia.
Initial purification of the aflatoxin B[1] synthesising
enzyme was achieved by separating the crude cell free extract by
gel filtration. The enzyme activity was located in a membrane
fraction. The involvement of endoplasmic reticulum was
indirectly concluded by the use of marker enzyme and chelating
agents. This membrane fraction was ultracentrifuged and the
released extrinsic proteins were separated by gel filtration.
A fraction containing two proteins which were capable
of converting sterigmatocystin to aflatoxin B[1] was isolated
and characterised by isoelectric focusing and gel electrophoresis. The temperature and pH optima together with the
cofactor
requirements were studied. The Michaelis-Menten constant
(Km) and the stoichiometry for the conversion of
sterigmatocystin to aflatoxin B[1] was determined.
Description
Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1984.
Keywords
Mycotoxins., Aflatoxins., Theses--Biochemistry.