Studies on L-asparagine metabolism in Aspergillus nidulans

Drainas, Constantine (1978) Studies on L-asparagine metabolism in Aspergillus nidulans. PhD thesis, University of Glasgow.

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A number of mutants (ahrA), resistant to the toxic analogue of L-asparagine, DL-aspartic acid-hydroxamate, have been isolated and shown to lack asparaginase I activity. The level of aspartic hydroxamate resistance is correlated with asparaginase I production, strongly resistant mutants have no detectable enzyme activity and weakly resistant ones have low enzyme activity. The enzyme activity of various heterozygous diploids containing the mutants indicated that gene expression is under strict dosage effect. It is proposed that asparaginase I is coded by the ahrA structural gene and asparaginase I activity is regulated by ammonia. This ammonia regulation requires protein synthesis and is either inactivation of enzyme activity vivo or repression of enzyme synthesis or both. A mutant epistatic to ahrA and tamA (a regulator gene responsible for the expression of a number of ammonia regulated systems), has been isolated. The existence of this mutant, named aspA20, and the fact that the ahrA mutants and the tamA50 mutant (completely repressed allele of the tamA locus) can utilise L-asparagine as a nitrogen source and as a carbon source respectively, strongly suggests the involvement of more than one enzyme in the utilisation of L-asparagine. An active transport system for L-asparagine has been detected in A. nidulans. This transport system is probably under nitrogen metabolite and carbon catabolite control. It is possible that an L-asparagine synthetase exists in A. nidulans which is coded by the asn-A1 gene.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: J A Pateman
Keywords: Microbiology, Physiology
Date of Award: 1978
Depositing User: Enlighten Team
Unique ID: glathesis:1978-72304
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 24 May 2019 15:12
Last Modified: 24 May 2019 15:12

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