Abstract
Regulation of the activity of the mitochondrial enzyme phosphatidylserine decarboxylase (PSD) was measured in vitro by using membrane preparations from wild-type and mutant strains of Saccharomyces cerevisiae. PSD specific activity was not affected by carbon source, and on all carbon sources, the highest specific activity was observed in cells entering the stationary phase of growth. However, PSD activity was found to be regulated in response to soluble precursors of phospholipid biosynthesis. PSD specific activity was reduced to about 63% of the level observed in unsupplemented wild-type cells when the cells were grown in the presence of 75 microM inositol. The presence of 1 mM choline alone had no repressing effect, but the presence of 1 mM choline and 75 microM inositol together led to further repression to a level of about 28% of the derepressed activity. Regulatory mutations known to affect regulation or expression of genes encoding phospholipid-synthesizing enzymes also affected PSD specific activity. opi1 mutants, which are constitutive for a number of phospholipid-biosynthetic enzymes, were found to have high, constitutive levels of PSD. Likewise, in ino2 or ino4 regulatory mutants, PSD activity was found to be at the fully repressed level regardless of growth condition. Regulation of PSD activity was also affected in several structural-gene mutants under conditions of impaired phosphatidylcholine biosynthesis. Together, these data strongly suggest that PSD expression is controlled by the mechanism of general control of phospholipid biosynthesis that regulates many enzymes of phospholipid biosynthesis.
Highlights
Regulation of the activity of the mitochondrial enzyme phosphatidylserine decarboxylase (PSD) was measured in vitro by using membrane preparations from wild-type and mutant strains of Saccharomyces cerevisiae
PSD is unique among the enzymes involved in PtdCho biosynthesis in that it cofractionates with the inner mitochondrial membrane [15, 29], whereas the phospholipid N-methyltransferases, for example, which catalyze the sequential methylation of PtdEtn that may be produced by the PSD reaction, are localized in the microsomal membrane
We have explored four aspects of the regulation of PSD: response to carbon sources affecting mitochondrial proliferation; response to growth in the presence or absence of soluble phospholipid precursors; effect of the regulatory mutations opil, ino2, and ino4; and requirement for ongoing PtdCho biosynthesis
Summary
Regulation of the activity of the mitochondrial enzyme phosphatidylserine decarboxylase (PSD) was measured in vitro by using membrane preparations from wild-type and mutant strains of Saccharomyces cerevisiae. A number of phospholipid-biosynthetic enzymes of Saccharomyces cerevisiae are subject to coordinate regulation These enzymes include cytidine diphosphate (CDP)-diacylglycerol synthase [12], phosphatidylserine (PtdSer) synthase [14, 21], inositol-1-phosphate synthase [11], and the phospholipid N-methyltransferases, which convert phosphatidylethanolamine (PtdEtn) into phosphatidylcholine (PtdCho) by three sequential methylations [10, 14, 23, 25, 27]. All of these enzymes exhibit a common pattern of regulation [5, 10]. PSD is unique among the enzymes involved in PtdCho biosynthesis in that it cofractionates with the inner mitochondrial membrane [15, 29], whereas the phospholipid N-methyltransferases, for example, which catalyze the sequential methylation of PtdEtn that may be produced by the PSD reaction, are localized in the microsomal membrane
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
