Pyruvate phosphatase

Ambasht, P.K. Malhotra, O.P. Kayastha, A.M. Purification, characterisation and steady state kinetic properties of cytosolic pyruvate kinase free of phosphoenol pyruvate phosphatase activity from germinating mung beans (Vigna radiata L.). Indian J. Biochem. Biophys., 33, 184-194 (1996)... 

Figure 2. Mechanism of PDH. The three different subunits of the PDH complex in the mitochondrial matrix (E, pyruvate decarboxylase E2, dihydrolipoamide acyltrans-ferase Ej, dihydrolipoamide dehydrogenase) catalyze the oxidative decarboxylation of pyruvate to acetyl-CoA and CO2. E, decarboxylates pyruvate and transfers the acetyl-group to lipoamide. Lipoamide is linked to the group of a lysine residue to E2 to form a flexible chain which rotates between the active sites of E, E2, and E3. E2 then transfers the acetyl-group from lipoamide to CoASH leaving the lipoamide in the reduced form. This in turn is oxidized by E3, which is an NAD-dependent (low potential) flavoprotein, completing the catalytic cycle. PDH activity is controlled in two ways by product inhibition by NADH and acetyl-CoA formed from pyruvate (or by P-oxidation), and by inactivation by phosphorylation of Ej by a specific ATP-de-pendent protein kinase associated with the complex, or activation by dephosphorylation by a specific phosphoprotein phosphatase. The phosphatase is activated by increases in the concentration of Ca in the matrix. The combination of insulin with its cell surface receptor activates PDH by activating the phosphatase by an unknown mechanism.

AP = alkaline phosphatase ATPase = adenosine triphosphatase Cardio = cardiovascular d = day(s) Endocr = endocrine F = female Gastro = gastrointestinal Gn pig = guinea pig GOT = glutamic-oxaloacetic transaminase GPT = glutamic-pyruvic transaminase Hemato = hematological hr = hour(s) LDH = lactate dehydrogenase LOAEL = lowest-observable-adverse-effect level M = male Musc/skel = musculoskeletal NOAEL = no-observable-adverse-effect level ... 

Product Acceptors. Many enzyme assays use acceptors, as for instance 2-ethylaminoethanol and other aminated alcohols iihich act as acceptors for the phosphoryl product of the reaction catalyzed by alkaline phosphatase (25) (Fig. 4). Hydroxylamine can act as an acceptor for the hydroxyacetone produced by eno-lase and semicarbazide can act as an acceptor for the pyruvate produced by LD. It is necessary to optimize the concentration of such an acceptor before using it routinely as often what may be a theoretically desirable acceptor is in practice superfluous. 

Figure 5 Model of phosphorus (P) deficiency-induced physiological changes associated with the release of P-mobilizing root exudates in cluster roots of white lupin. Solid lines indicate stimulation and dotted lines inhibition of biochemical reaction sequences or mclaholic pathways in response to P deliciency. For a detailed description see Sec. 4.1. Abbreviations SS = sucrose synthase FK = fructokinase PGM = phosphoglueomutase PEP = phosphoenol pyruvate PE PC = PEP-carboxylase MDH = malate dehydrogenase ME = malic enzyme CS = citrate synthase PDC = pyruvate decarboxylase ALDH — alcohol dehydrogenase E-4-P = erythrosc-4-phosphate DAMP = dihydraxyaceConephos-phate APase = acid phosphatase.

The free glucose produced by this reaction is supplied to the blood from the tissues. As exemplified by gluconeogenesis, one may easily envision the economical organization of these metabolic routes, since, apart from four special gluconeogenesis enzymes-pyruvate carboxylase, phosphopyruvate carboxylase, fructose bisphosphatase, and glucose 6-phosphatase-individual glycolytic enzymes are also used in the gluconeogenesis. 

Fig. 14.2. Regulation of the pyruvate dehydrogenase complex (PDC) from adult A suum muscle. PDC, pyruvate dehydrogenase complex E1, pyruvate dehydrogenase subunit of the PDC PDK, pyruvate dehydrogenase kinase PDP, pyruvate dehydrogenase phosphatase.

Chen, G., Wang, L., Liu, S., Chuang, C. and Roche, T.E. (1996) Activated function of the pyruvate dehydrogenase phosphatase through Ca2+-facilitated binding to the inner lipoyl domain of the dihydrolipoyl acetyltransferase. Journal of Biological Chemistry 271,28064-28070. 

Huang, B., Gudi, R., Wu, P., Harris, R.A., Hamilton, J. and Popov, KM. (1998a) Isoenzymes of pyruvate dehydrogenase phosphatase. DNA-derived amino acid sequences, expression, and regulation. Journal of Biological Chemistry 273, 17680-17688. 

Song, H. and Komuniecki, R. (1994) Novel regulation of pyruvate dehydrogenase phosphatase purified from anaerobic muscle mitochondria of the adult parasitic nematode, Ascaris suum. Journal of Biological Chemistry 269, 31573-31578. 

Yang, D., Gong, X., Yakhnin, A. and Roche, T.E. (1998) Requirements for the adaptor protein role of dihydrolipoyl acetyltransferase in the up-regulated function of the pyruvate dehydrogenase kinase and pyruvate dehydrogenase phosphatase. Journal of Biological Chemistry 273, 14130-14137. 

The PDHC catalyzes the irreversible conversion of pyruvate to acetyl-CoA (Fig. 42-3) and is dependent on thiamine and lipoic acid as cofactors (see Ch. 35). The complex has five enzymes three subserving a catalytic function and two subserving a regulatory role. The catalytic components include PDH, El dihydrolipoyl trans-acetylase, E2 and dihydrolipoyl dehydrogenase, E3. The two regulatory enzymes include PDH-specific kinase and phospho-PDH-specific phosphatase. The multienzyme complex contains nine protein subunits, including... 

In biological systems, therefore, the behavior of Li+ is predicted to be similar to that of Na+ and K+ in some cases, and to that of Mg2+ and Ca2+ in others [12]. Indeed, research has demonstrated numerous systems in which one or more of these cations is normally intrinsically involved, including ion transport pathways and enzyme activities, in which Li+ has mimicked the actions of these cations, sometimes producing inhibitory or stimulatory effects. For example, Li+ can replace Na+ in the ATP-dependent system which controls the transport of Na+ through the endoplasmic reticulum Li+ inhibits the activity of some Mg2+-dependent enzymes in vitro, such as pyruvate kinase and inositol monophosphate phosphatase Li+ affects the activity of some Ca2+-dependent enzymes— it increases the levels of activated Ca2+-ATPase in human erythrocyte membranes ex vivo and inhibits tryptophan hydroxylase. 

F (increases in alkaline phosphatase(48%), glutamate oxaloacetate transaminase (82%) glutamate pyruvate transaminase (55%), isocitrate dehydrogenase (65%), cholesterol (27%-35%), and soluble proteins (35%) decreases in free amino acids (34-40%) and glucose (41-51%) vacuolization fatty infiltration)... 

PDH is a multi-enzyme complex consisting of three separate enzyme units pyruvate decarboxylase, transacetylase and dihydrolipoyl dehydrogenase. Serine residues within the decarboxylase subunit are the target for a kinase which causes inhibition of the PDH the inhibition can be rescued by a phosphatase. The PDH kinase (PDH-K) is itself activated, and the phosphatase reciprocally inhibited, by NADH and acetyl-CoA. Figure 3.12(a and b) show the role and control of PDH. 

Control of pymvate dehydrogenase activity is via covalent modification a specific kinase causes inactivation of the PDH by phosphorylation of three serine residues located in the pyruvate decarboxylase/dehydrogenase component whilst a phosphatase activates PDH by removing the phosphates. The kinase and phosphatase enzymes are non-covalently associated with the transacetylase unit of the complex. Here again we have an example of simultaneous but opposite control of enzyme activity, that is, reciprocal regulation. 

Interconversion processes (see p. 120) also play an important role. They are shown here in detail using the example of the PDH complex (see p. 134). The inactivating protein kinase [la] is inhibited by the substrate pyruvate and is activated by the products acetyl-CoA and NADH+H. The protein phosphatase [Ibj—like isodtrate dehydrogenase [3] and the ODH complex [4j-is activated by Ca. This is particularly important during muscle contraction, when large amounts of ATP are needed. Insulin also activates the PDH complex (through inhibition of phosphorylation) and thereby promotes the breakdown of glucose and its conversion into fatty acids. 

This phosphatase [EC 3.1.3.60] catalyzes the hydrolysis of phosphoenolpyruvate to form pyruvate and phos-... 

Following intravenous injection of 0-2.8 pCi/kg (104,000 Bq/kg) thorium-227 in a solution of citric acid-sodium citrate buffer in dogs, an increase in serum alkaline phosphatase measurements and hypoalbuminemia and hyperglobulinemia were observed (Stevens et al. 1967). No effects on the levels of serum glutamic pyruvic transaminase (SGPT) or serum glutamic oxaloacetic transaminase (SGOT) were found. 

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