Activation of yeast pyruvate carboxylase: interactions between acyl coenzyme A compounds, aspartate, and substrates of the reaction

Abstract

Chicken liver pyruvate carboxylase has an absolute requirement for short-chain acyl coenzyme A (CoA), whereas the same enzyme from yeast has less stringent requirements. The yeast enzyme has now been studied in an effort to elucidate the mechanism by which acyl-CoA stimulates pyruvate carboxylase activity. Yeast pyruvate carboxylase has an apparent basal level of activity above which CoA and acyl-CoAs of 2-20 carbons activate; the concentration of acyl-CoA required for half-maximum activation (K0.5) decreases as the chain length of the acyl moiety increases to 16 carbons. Activation of yeast pyruvate carboxylase by acyl-CoA is brought about in part by increasing the affinity of pyruvate carboxylase for two substrates, bicarbonate and pyruvate. The affinity of pyruvate carboxylase for bicarbonate is also increased by potassium ions. The observation of only low levels of activity in the absence of acyl-CoA or potassium ion leads to the conclusion that the basal activity so frequently referred to is probably due to the presence of activating monovalent cations. Pyruvate carboxylase from yeast probably has an absolute requirement for monovalent cations or acyl-CoA with a combination of the two being required for optimum conditions for maximal activity. Stimulation by acyl-CoA and inhibition by aspartate are mutually antagonistic with each affecting the activation or inhibition constant and the degree of cooperativity brought about by the other. The enzyme from liver is unaffected by aspartate.

Tissue-specific overexpression of lipoprotein lipase causes tissue-specific insulin resistance

“…This finding parallels the results in the muscle-LPL mice and suggests that the defect in liver insulin signaling in the liver-LPL mice may also be because of an alteration in insulin signaling at the level of the insulin receptor substrates. In addition, it is possible that accumulation of fatty acyl CoA, a known activator of pyruvate carboxylase (25), leads to a relative increase in hepatic gluconeogenesis without an increase in overall rates of EGP. Because glycogenolysis is more sensitive to insulin's action than gluconeogenesis (26), this would further contribute to hepatic unresponsiveness during the hyperinsulinemic-euglycemic clamp.…”

Regulation of the structure and activity of pyruvate carboxylase by acetyl CoA

“…The antagonistic effects between L-aspartate and acyl CoAs has been well documented in PC from S. cerevisiae [13, 43], Aspergillus nidulans [44] and S. aureus [18]. In PC from A. nidulans , Osmani et al [44] determined that acetyl CoA has an activating effect on the pyruvate carboxylation reaction only in the presence of L-aspartate.…”

“…Further, acyl CoA analogs of acetyl CoA will stimulate the carboxylation activity of PC from a variety of sources, although the degree of activation is usually not as significant as it is with acetyl CoA. In general, PCs that are localized in the cytosol, including those from Saccharomyces cerevisiae [13-15] and Rhizopus arrhizus [16], exhibit a preference for longer chain acyl CoAs. Alternatively, PCs from some bacteria, including those from Thiobacillus novellus [17], Staphylococcus aureus [18], Bacillus thermodenitrificans [19], and those which are localized in the mitochondria such as chicken [20] and rat liver [21] are activated to a greater extent by shorter chain acyl CoAs.…”

Inhibitors of Pyruvate Carboxylase~!2009-12-01~!2010-02-01~!2010-04-15~!

“…The aspartate inhibition kinetics are complex, typically exhibiting non-classical behaviour. PC from S. cerevisiae is inhibited by aspartate in the presence of the activators acetyl CoA or palmitoyl CoA, with the addition of 10 mM aspartate resulting in a 70- to 80-fold increase in the activator concentration required for half-maximal activation [96]. In fungi, the aspartate allosteric binding site appears to be distinct from the site of acetyl CoA binding, despite the observed competitive inhibition of acetyl CoA by aspartate [95, 98].…”