Pyruvate dehydrogenase kinase activity of pig heart pyruvate dehydrogenase (E1 component of pyruvate dehydrogenase complex)

Probing the mechanism of inactivation of human pyruvate dehydrogenase by phosphorylation of three sites

Activity of the mammalian pyruvate dehydrogenase complex (PDC) is regulated by phosphorylation-dephosphorylation of three serine residues (designated site 1, Ser-264; site 2, Ser-271; site 3, Ser-203) in the alpha subunit of the pyruvate dehydrogenase (E1) component. Substitutions of the phosphorylation sites were generated by site-directed mutagenesis. Glutamate (S1E) and aspartate (S1D) substitutions at site 1 resulted in the complete loss of PDC activity; however, these mutants were variably active in the decarboxylation and 2,6-dichlorophenolindophenol assays. S1Q had only 3% of wild-type PDC activity. The apparent K(m) values for pyruvate increased for the mutants of site 1 when determined in the 2,6-dichlorophenolindophenol assay. The substitutions at sites 2 and 3 caused only moderate reductions in activity in the three assays. S3E had a 27-fold increase in the apparent K(m) for thiamine pyrophosphate and 8-fold increase in the K(i) for pyrophosphate. Site 3 was almost completely protected from phosphorylation by thiamine pyrophosphate. The results show that the size rather than negative charge of the substituted amino acid residue affects the active site of E1 and that modification of each of the three serine residues affect the active site in a site-specific manner for its ability to bind the cofactor and substrates.

Regulation of mammalian pyruvate dehydrogenase kinase

It is generally believed that mammalian pyruvate dehydrogenase kinase is a heterodimer consisting of catalytic and regulatory subunits. However, the contribution of the two subunits to the kinase-mediated signal transduction has remained undefined. In the present study recombinant components of mammalian pyruvate dehydrogenase complex were employed in order to characterize the role of the kinase catalytic subunit in the regulation of pyruvate dehydrogenase reaction. The results provide the first evidence strongly suggesting that the catalytic subunit of pyruvate dehydrogenase kinase is competent to respond to known effectors of kinase activity as well as to interact with the E2-core without assistance of a regulatory subunit.

Effects of pyruvate on pyruvate dehydrogenase kinase of rat heart

Sensitivity of rat heart pyruvate dehydrogenase kinase (PDHK) to pyruvate inhibition was tested under various conditions using pyruvate dehydrogenase complex (PDC) in mitochondria (mPDC) and in a high speed precipitate of whole tissue homogenates (hPDC). In the latter preparation pyruvate in the range of concentration 1-10 mM caused increasing inhibition of PDHK when the enzyme was prepared from animals fed ad libitum but had no effect when the enzyme was prepared from 48 h starved animals. Similar behaviour was observed in mPDC from fed and starved animals when rotenone was present, pyruvate at 1 mM concentration stimulated PDHK from hearts of fed animals but was without effect at 10 mM. When mPDC or hPDC from hearts of starved animals was incubated at 30 degrees C for 30 min, inhibition of PDHK by pyruvate was restored.

Mutagenesis studies of the phosphorylation sites of recombinant human pyruvate dehydrogenase. Site-specific regulation

Mammalian pyruvate dehydrogenase (alpha 2 beta 2) (E1) is regulated by phosphorylation-dephosphorylation, catalyzed by the E1-kinase and the phospho-E1-phosphatase. Using site-directed mutagenesis of the three phosphorylation sites (sites 1, 2, and 3) on E1 alpha, several human E1 mutants were made with single, double, and triple mutations by changing Ser to Ala. Mutation at site 1 but not at sites 2 and/or 3 decreased E1 specific activity and also increased Km values for thiamin pyrophosphate and pyruvate. Sites 1, 2, and 3 in the E1 mutants were phosphorylated either individually or in the presence of the other sites by the dihydrolipoamide acetyltransferase-protein X-E1 kinase indicating a site-independent mechanism of phosphorylation. Phosphorylation of each site resulted in complete inactivation of the E1. However, the rates of phosphorylation and inactivation were site-specific. Sites 1, 2, and 3 were dephosphorylated either individually or in the presence of the other sites by the phospho-E1-phosphatase resulting in complete reactivation of the E1. The rates of dephosphorylation and reactivation were similar for sites 1, 2, and 3, indicating a random dephosphorylation mechanism.

Role of protein synthesis and of fatty acid metabolism in the longer-term regulation of pyruvate dehydrogenase kinase

Antibodies were raised in rabbits to free rat liver pyruvate dehydrogenase (PDH) kinase alpha-chain and shown to react with PDH kinase alpha-chain in rat heart and liver PDH complexes, in purified pig heart PDH complex and in bovine kidney dihydrolipoamide acetyltransferase-protein X-PDH kinase subcomplex. E.l.i.s.a for PDHE1 (pyruvate dehydrogenase) and PDH kinase have been developed and applied to assays of these proteins in extracts of rat liver and rat heart mitochondria; the measured immunoreactivities for PDHE1 (heart > liver) and for PDH kinase alpha-chain (liver > heart) paralleled known differences in PDH complex and PDH kinase activities respectively. The results of e.l.i.s.a of PDH kinase alpha-chain in extracts of rat liver mitochondria showed that the effects of starvation to increase PDH kinase activity in vivo, and the effects of dibutyryl cyclic AMP or palmitate to increase PDH kinase activity in hepatocytes cultured in vitro, are due largely (> 90%) to an increase in the specific activity of PDH kinase. The effect, in cultured hepatocytes, of dibutyryl cyclic AMP to increase PDH kinase activity was blocked by cycloheximide; the effect of palmitate was blocked by an inhibitor of carnitine palmitoyltransferase I (Etomoxir), but not by cycloheximide.

Purification and partial characterization of rat liver pyruvate dehydrogenase kinase activator protein (free pyruvate dehydrogenase kinase)

Rat liver pyruvate dehydrogenase (PDH) kinase activator protein (KAP), a free PDH kinase readily separable from PDH complex and its intrinsic kinase, has been purified to apparent homogeneity from liver mitochondria of fed and 48-h starved rats. On SDS-PAGE an apparently single band of M(r) 45 kDa was obtained. N-Terminal amino acid sequence analyses (8-10 cycles) confirmed the presence of a single peptide in each case. The specific activity of the purified KAP from 48-h starved rats (14,413 U/mg protein) was 4.5-fold greater than that from fed rats.

Evidence that rat liver pyruvate dehydrogenase kinase activator protein is a pyruvate dehydrogenase kinase

It is shown here that rat liver pyruvate dehydrogenase (PDH) kinase activator protein (KAP) catalyses ATP-dependent inactivation and [32P]phosphorylation of pig heart PDHE1 and of yeast (Saccharomyces cerevisiae) PDH complex devoid of PDH kinase activity, that fluorosulphonylbenzoyladenosine inactivates rat liver KAP and the intrinsic PDH kinase of rat liver PDH complex, and that KAP, like PDH kinase, is inactivated by thiol-reactive reagents. It is concluded that KAP is a free PDH kinase.

Effect of dichloroacetate on oxidative removal of lactate in mice after supramaximal exercise

1. The effect of dichloroacetate (DCA), which activates substrate oxidation on oxidative removal of lactate in mice after supramaximal exercise was investigated. 2. DCA significantly decreased the blood lactate concentration and increased the oxidative removal of lactate during prolonged exercise. 3. No significant differences were found in the removal of the blood lactate concentration, in oxidative removal of lactate after supramaximal exercise. 4. It is concluded that DCA administration which activates lactate oxidation during exercise does not activate lactate oxidation in mice after supramaximal exercise.

Kinase activator protein mediates longer-term effects of starvation on activity of pyruvate dehydrogenase kinase in rat liver mitochondria

Starvation of rats for 48 h increased the activity of PDH (pyruvate dehydrogenase) kinase 2.2-fold in extracts of liver mitochondria, 2.9-fold in PDH complex partially purified therefrom by fractional precipitation, and 5-fold in PDH complex partially purified by gel filtration on Sephacryl S-300. A protein fraction was separated from PDH complex in extracts of rat liver mitochondria by gel filtration or fractional precipitation, which increased the activity of PDH kinase in rat liver and pig heart PDH complexes. The activity of this protein fraction was increased approx. 2.5-fold by 48 h starvation of rats. With highly purified pig heart PDH complex it was shown that the protein fraction increased the Vmax. of the PDH kinase reaction 35-fold (fraction from fed rats) or 82-fold (fraction from starved rats); starvation had no effect on the concentration of protein fraction required to give 0.5 Vmax. Evidence is given that the increase in PDH kinase activity effected in extracts of liver mitochondria by starvation is due to increased activity of kinase activator protein, which is tightly bound by rat liver PDH complex and not removed by a single gel filtration. With pig heart PDH complex, increased PDH kinase activity was retained after gel filtration of an admixture with kinase activator protein from starved rats, but was restored to the control value by a second gel filtration; the alterations in PDH kinase activity were associated with obvious changes in protein bands in SDS gels.