Succinyl-CoA Synthetase Is a Phosphate Target for the Activation of Mitochondrial Metabolism

Publisher Website
Google Scholar
Abstract
Succinyl-CoA synthetase (SCS) is the only mitochondrial enzyme capable of ATP production via substrate level phosphorylation in the absence of oxygen, but it also plays a key role in the citric acid cycle, ketone metabolism, and heme synthesis. Inorganic phosphate (Pi) is a signaling molecule capable of activating oxidative phosphorylation at several sites, including NADH generation and as a substrate for ATP formation. In this study, it was shown that Pi binds the porcine heart SCS α-subunit (SCSα) in a noncovalent manner and enhances its enzymatic activity, thereby providing a new target for Pi activation in mitochondria. Coupling 32P labeling of intact mitochondria with SDS gel electrophoresis revealed that 32P labeling of SCSα was enhanced in substrate-depleted mitochondria. Using mitochondrial extracts and purified bacterial SCS (BSCS), we showed that this enhanced 32P labeling resulted from a simple binding of 32P, not covalent protein phosphorylation. The ability of SCSα to retain its 32P throughout the SDS denaturing gel process was unique over the entire mitochondrial proteome. In vitro studies also revealed a Pi-induced activation of SCS activity by more than 2-fold when mitochondrial extracts and purified BSCS were incubated with millimolar concentrations of Pi. Since the level of 32P binding to SCSα was increased in substrate-depleted mitochondria, where the matrix Pi concentration is increased, we conclude that SCS activation by Pi binding represents another mitochondrial target for the Pi-induced activation of oxidative phosphorylation and anaerobic ATP production in energy-limited mitochondria.