Enzyme redundancy in yeast: genetical and biochemical studies on two glutamate dehydrogenase (NADP) isozymes.

DELUNA, A.; AVENDAÑO, A.; RIEGO, L.; GONZALEZ, A.

Praga, República Checa.

Congreso; XX International Conference on Yeast Genetics and Molecular Biology; 2001

Federation of European Microbiological Societies

Saccharomyces cerevisiae shows a considerable fraction of duplicated genes resulting from an ancient whole genome duplication, and most of the homologues share the original function. Yeast ammonium assimilation and glutamate biosynthetic pathways are redundant, and primarily achieved by the amminating glutamate dehydrogenase (NADP-GDH). In S. cerevisiae, this pathway is mediated by two isozymes coded by GDH1 and GDH3, which share 86% amino acid identity. In order to obtain detailed information, which could explain the conservation of apparently redundant functions, we analyzed the NADP-GDH isozymes at various functional levels. Our results showed a differential expression depending on carbon source. Disruption mutant analysis indicated that although glutamate biosynthesis depends primarily on GDH1 when grown on glucose, both genes must be intact for normal growth on ethanol. On the other hand, the purified isozymes showed different stability and kinetic properties, particularly in what respects to their apparent affinity for 2-oxoglutarate, and competitive phosphate inhibition. This results suggest that the presence of two different biosynthetic GDH isozymes may represent the possibility to modulate this activity under the different metabolic conditions given by carbon source, and point to the importance of the NADP-GDH pathway as a node between carbon and nitrogen metabolism.