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

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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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
Divisions: Schools > School of Science and Technology
Record created by: Jeremy Silvester
Date Added: 17 Sep 2020 13:37
Last Modified: 19 Jul 2023 09:47

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