Species: Pisum sativum
Subunit composition of pyruvate dehydrogenase complex = [pyruvate dehydrogenase][dihydrolipoyl transacetylase][dihydrolipoyl dehydrogenase]
The Pisum sativum pyruvate dehydrogenase complex catalyzes the conversion of pyruvate to acetyl-CoA and CO2. It contains multiple copies of three enzymatic components: pyruvate decarboxylase (E1), lipoamide acyltransferase (E2) and lipoamide dehydrogenase (E3).
This enzyme belongs to the family of 2-oxo acid dehydrogenase complexes. To learn more about this enzyme family, see 2-oxoisovalerate decarboxylation to isobutanoyl-CoA.
In Gram-positive bacteria and mitochondria the E1 component is a heterodimer composed of two subunits, while in Gram-negative bacteria it is made up of a single type of subunit. In both cases multiple copies of the E1 component, along with multiple copies of the E3 component, are assembled around an E2 core of icosahedral symmetry (24 subunits for bacteria, 60 subunits for eukaryotes).
Plants have two forms of pyruvate dehydrogenase complex, one in the plastid and the other in the mitochondrion. The two complexes have distinct physiological roles. The plastid pyruvate dehydrogenase complex provides the main acetyl-CoA source for de novo fatty acid biosynthesis. The mitochondrial complex provides acetyl-CoA for the TCA cycle and NADH for oxidative phosphorylation. Both complexes are feedback inhibited by acetyl-CoA and NADH. However the two complexes differ in other aspects of enzyme characteristics [TovarMendez03, Nikolau00, Fatland00].
The pea plastid pyruvate dehydrogenase complex was partially purified and the catalytic activities was characterized for the complex [Camp85, Camp88]. The molecular weight of the complex and the exact subunit composition of it could not be resolved.
Enzymatic reaction of: pyruvate dehydrogenase
EC Number: 1.2.1.-pyruvate + coenzyme A + NAD+ ⇄ acetyl-CoA + CO2 + NADH
The direction shown, i.e. which substrates are on the left and right sides, is in accordance with the direction in which it was curated.
This reaction is reversible.
NADP+ could only slightly replace NAD+, giving a rate of 4% of that with NAD+. Divalent cation is required for the enzyme activity. Mg2+ is the most effective cation. The Km with Mg2+ is 1 mM [Camp85].
The products of the reaction, NADH and acetyl-CoA, inhibit the enzyme activity. NADH and acetyl-CoA are uncompetitive inhibitors with respect to pyruvate, and competitive inhibitors with respect to CoA and NAD, respectively. Acetyl-CoA is a non-competitive inhibitor with respect to NAD, so is NADH with respect to CoA [Camp88].palmitate [Camp88] Inhibitors (Unknown Mechanism): acetyl-CoA [Camp88], NADH [Camp88], oleate [Camp88]
pH(opt): 8 [Camp85]
Camp88: Camp, Pamela J, Miernyk, Jan A, Randall, Douglas D (1988). "Some kinetic and regulatory properties of the pea chloroplast pyruvate dehydrogenase complex." Biochimica et Biophysica Acta, 933:269-275.
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