α-Keto acid dehydrogenase complexes

Activation of pyruvate dehydrogenase in adipose tissue by insulin. Evidence for an effect of insulin on pyruvate dehydrogenase phosphate phosphatase

“…At present there are three factors known to affect pyruvate dehydrogenase phosphate phosphatase activity: Mg2+ (Linn et al, 1969a); Ca2+ (Denton et al, 1972;Hucho et al, 1972: Siess & Wieland, 1972; and free citrate (Taylor & Halperin, 1973). Whether any of these factors is involved in the slowly reversible activation of pyruvate dehydrogenase phosphate phosphatase by insulin is not known.…”

“…1. We assume that this rise in activity is the result ofenzymic dephosphorylation of pyruvate dehydrogenase phosphate, a process which has been carefully studied in Reed's laboratory (Linn et al, 1972;Hucho et al, 1972).…”

“…From these requirements, we assumed that the declining dehydrogenase activity is the result of an enzymic phosphorylation of pyruvate dehydrogenase, as studied in detail in Reed's laboratory (Linn et al, 1972;Hucho et al, 1972). Using this system as an assay for pyruvate dehydrogenase kinase in tissue extracts we have been unable to demonstrate any effect of insulin or adrenaline treatment of tissue segments.…”

“…Further, neither the pyruvate dehydrogenase kinase or the pyruvate dehydrogenase phosphate phosphatase appear to be directly affected by cyclic AMP or cyclic GMP (Jungas, 1971;Hucho et al, 1972;Siess & Wieland, 1972;Randle & Denton, 1973). As a first step in exploring the mechanisms by which insulin might influence the degree of phosphorylation of this mitochondrial protein, we have sought to determine whether it is the pyruvate dehydrogenase kinase, the pyruvate dehydrogenase phosphate phosphatase, or both whose activity is modulated by the hormone.…”

The control of tricarboxylate-cycle oxidations in blowfly flight muscle. The steady-state concentrations of coenzyme A, acetyl-coenzyme A and succinyl-coenzyme A in flight muscle and isolated mitochondria

“…These differences are reproducible and suggest that the pyruvate dehydrogenase complex is considerably more active at 2.5mM-pyruvate than at 0.44mM-pyruvate, which is somewhat surprising in view of the Km of 0.1mM obtained for the solubilized and partially purified enzyme from this tissue (R. G. Hansford, unpublished work). Conceivably, the pyruvate functions to protect the complex against phosphorylation (Hucho et al, 1972) though it is equally possible that the substrate affinity of the enzyme is altered by removal from its mitochondrial environment. Repetition of this experiment at a lower phosphate concentration gave the results shown in Fig.…”