Physiological consequences of loss of allosteric activation of yeast NAD+-specific isocitrate dehydrogenase.
Abstract
Based on allosteric regulatory properties, NAD+-specific isocitrate dehydrogenase (IDH) is believed to control flux through the tricarboxylic acid cycle in vivo. To distinguish growth phenotypes associated with regulatory dysfunction of this enzyme in Saccharomyces cerevisiae, we analyzed strains expressing well defined mutant forms of IDH or a non-allosteric bacterial NAD+-specific isocitrate dehydrogenase (IDHa). As previously reported, expression of mutant forms of IDH with severe catalytic defects but intact regulatory properties produced an inability to grow with acetate as the carbon source and a dramatic increase in the frequency of generation of petite colonies, phenotypes also exhibited by a strain (idh1Deltaidh2Delta) lacking IDH. Reduced growth rates on acetate medium were also observed with expression of enzymes with severe regulatory defects or of the bacterial IDHa enzyme, suggesting that allosteric regulation is also important for optimal growth on this carbon source. However, expression of IDHa produced no effect on petite frequency, suggesting that the intermediate petite frequencies observed for strains expressing regulatory mutant forms of IDH are likely to correlate with the slight reductions in catalytic ef...Continue Reading
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