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PubMed1975

The pyruvate-dehydrogenase complex from Azotobacter vinelandii. 2. Regulation of the activity.

The presence of activators(AMP and sulphate) or inhibitors(acetyl-CoA) has no influence on the Hill coefficient of the S-shaped [pyruvate]--velocity curve of either the pyruvate-NAD+ overall reaction(h equals 2.5) or that of the pyruvate-K3Fe(CN)6 ACTIVITY OF THE FIRST ENZYME (H EQUALs 1.3). pH STUDIES INDICATED THAT THE Hill coefficient is dependent on subunit ionization within the pyruvate-containing complex and not on those in the free complex. It is concluded that pyruvate conversion rather that pyruvate binding is responsible for the allosteric pattern. The activity is due to absence of a protein kinase, mainly regulated at the acetyl-CoA/CoA, and NADH/NAD+ levels and by the value of the energy charge.

Acetyl Coenzyme A↗
PubMed1990

Changes in the core of the mammalian-pyruvate dehydrogenase complex upon selective removal of the lipoyl domain from the transacetylase component but not from the protein X component.

The dihydrolipoyl transacetylase (E2) component contains a COOH-terminal inner domain (E2I) and an extended NH2-terminal structure, which is composed of two lipoyl domains (the fragment containing both is designated as E2L) and a subunit-binding domain (E2B). The four domains are connected by hinge regions. A subcomplex, composed of an oligomer of E2 subunits, protein X (which also has an NH2-terminal lipoyl domain), and the [pyruvate dehydrogenase]-kinase catalytic and basic subunits (Kc and Kb, respectively) (i.e. E2.X.KcKb subcomplex), was treated with Clostridium histolyticum collagenase. E2 subunits were selectively cleaved at the NH2-terminal end of the E2B domain, releasing the E2L fragment. Complete release of E2 subunits also released the kinase subunits, indicating that the kinase is bound to the E2L portion of E2. The residual inner core subcomplex (designated E2IB.X) has a strong tendency to aggregate, but this can be reversed with heparin (1 mg/ml). The E2IB.X subcomplex binds the pyruvate dehydrogenase (E1) and dihydrolipoyl dehydrogenase (E3) components. The E1 component, which binds to the E2B domain, blocked collagenase cleavage of E2. We evaluated the capacity of the collagenase-treated E2.X.KcKb subcomplex, from which different portions of the E2L domains were removed, to support (in combination with excess levels of the E1 and E3 components) the overall reaction of the complex. Loss of activity occurred only after more than half of the E2L domains were removed. This delay is in sharp contrast to the effect of selective removal of the lipoyl domain of protein X, which leads to an immediate decrease in activity (Gopalakrishnan, S., Rahmatullah, M., Radke, G.-A., Powers-Greenwood, S. L., and Roche, T. E. (1989) Biochem. Biophys. Res. Commun. 160, 715-721). These results suggest that multiple lipoyl domains of the E2 component service the rate-limiting E1 component. After all the E2L domains were removed and the E2IB.X subcomplex was separated from free E2L, 10% activity was retained in the overall reaction. Thus, the lipoyl domain of protein X supported the overall reaction of the complex.

Acetyltransferases↗
PubMed2001

The disruption of a gene encoding a putative arylesterase impairs pyruvate dehydrogenase complex activity and nitrogen fixation in Sinorhizobium meliloti.

Nitrogen-fixing Sinorhizobium meliloti cells depend upon dicarboxylic acids as carbon and energy sources. The metabolism of these intermediate compounds of the trichloroacetic acid cycle is dependent upon the availability of acetyl-coenzyme A (CoA). In bacteroids, the combined activities of malic enzymes and pyruvate dehydrogenase (PDH) have been proposed to be responsible for the anaplerotic synthesis of acetyl-CoA. We obtained a S. meliloti mutant strain, PD3, in which a Tn5 insertion led to a significant decrease in the overall PDH activity. The genetic characterization of this mutant revealed that the transposon is located at the 3' end of a gene (ada) encoding a putative arylesterase. The mutant PD3 is deficient in nitrogen fixation, which strengthens the physiological importance of PDH activity in the symbiosis of S. meliloti with alfalfa plants.

Acetyl Coenzyme A↗