An investigation into the metabolism of the important mycotoxins produced by Aspergillus species.

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Anderson, M.S., 1978. An investigation into the metabolism of the important mycotoxins produced by Aspergillus species. PhD, Nottingham Trent University.

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Abstract

Various potential intermediates involved in aflatoxin biosynthesis have been isolated in preparation as substrates for cell-free extracts; several other compounds have also been isolated but their structures have yet to be fully confirmed.

Using a number of conventional techniques to obtain cell-free extracts, i.e. homogenization, sonication, liquid nitrogen and lypholization, it has been shown that the enzymes involved in aflatoxin biosynthesis are extremely labile and that a delicate method of cell-free extract isolation is required.

In order to obtain an active cell-free extract, protoplasts have been prepared by enzymically digesting away the cell wall. Whole protoplasts behave in a manner similar to the whole mycelium but with a reduced aflat ox in-producing potential, this is probably due to protoplasts in the idiophase reverting back to the tropophase. The whole protoplasts are capable of converting some potential intermediates into aflatoxins, e.g. versicolorin A and C, versiconal acetate and sterigmatocystin, but not averufin, O-methylsterigmatocystin or norsolorinic acid; this may indicate that none of these latter compounds are true intermediates. Lysis of the protoplasts, by osmotic tension and freezing, has yielded a cell-free extract capable of converting versiconal acetate, but not versicolorin A, to aflatoxin B1. This suggests that versicolorin A is not a true intermediate in aflatoxin biosynthesis and that it may only be a "side-shunt" molecule.

Other results indicate that an FAD-linked oxygenase(s) is involved in aflatoxin biosynthesis. It is also shown that a nicotinamide-linked oxygenase is involved in versicolorin A production and that the general esterase activity of a cell-free extract from a versicolorin A-producing mutant is inhibited by dichlorvos. It is also suggested that a hydroxy derivative of versicolorin A is involved in aflatoxin biosynthesis and a biosynthetic pathway incorporating these results is outlined.

Item Type:

Thesis

Creators:

Anderson, M.S.

Date:

1978

ISBN:

9781369313925

Identifiers: