Kinetic and molecular characteristics of allosteric pyruvate kinase from muscle tissue of the sea mussel Mytilus edulis L

Characterization of pyruvate kinase of Trypanosoma brucei and its role in the regulation of carbohydrate metabolism

Pyruvate kinase from Trypanosoma brucei is a labile enzyme, losing its activity within several hours. In mixtures containing 50 mM triethanolamine buffer, pH 7.2, 25% glycerol and 0.5 mM inorganic phosphate the enzyme remained active and could be purified to homogeneity with a specific activity of 417 units mg-1 and a yield of 65%. The enzyme has an activation energy of 31.9 kJ mol-1. Magnesium and potassium ions are essential for activity. Cobalt or manganese ions replace Mg2+ but this leads to a decrease in maximal velocity. Potassium ions can be substituted by ammonium ions, while sodium ions behave as a competitive inhibitor with respect to both K+ and NH4+. All metal ions studied displayed sigmoidal kinetics. The enzyme is activated, with decreasing efficiency by fructose 2-phosphorothioate 6-phosphate, fructose 2,6-bisphosphate, fructose 1,6-bisphosphate and glucose 1,6-bisphosphate. They all display hyperbolic kinetics. Glycerate 2,3-bisphosphate, glyceraldehyde 3-phosphate, CoASAc, oxalate, AMP, ADP, and ATP inhibit the enzyme. At substrate saturation PK was activated by Pi up to a concentration of 0.8 mM. At higher Pi concentrations the enzyme is inhibited. The enzyme is unaffected by most amino acids, only phenylalanine stimulates and tyrosine inhibits.

Pyruvate kinase isoenzymes in marine invertebrates: a comparative study by the use of monoclonal antibodies

1. Six monoclonal antibodies specific to the pyruvate kinase from the foot muscle of the common limpet P. caerulea were produced. 2. They also exhibited specificity against the mouse liver where the L-type isoenzyme of pyruvate kinase is present. They did not react with the mouse skeletal muscle, heart or red blood cells isoenzymes of pyruvate kinase (PK). One of these, the monoclonal antibody B did not react with any PK isoenzymes of the mouse tissues. 3. The presence of the isoenzymic type of PK which was recognized by the monoclonals, (type L), was traced in five phyla of marine invertebrates by the application of the monoclonal antibodies A, B and C. 4. In two phyla the majority of the animals were found to possess an L-type PK isoenzyme in their muscles while in quite a few of them a different isoenzymic type was present in the other tissues. The results of this study are compared with the existing literature, and the use of monoclonal antibodies in the study of enzymic systems is considered in the discussion.

In vivo and in vitro studies on the pathway of modification of mussel pyruvate kinase

1. On aerial exposure, pyruvate kinase is inactivated in various organs of M. edulis; the decrease of activity is slower in muscle than in non-muscular tissue. 2. Anoxic in vitro incubation of gills results in a rapid inactivation of pyruvate kinase. No change occurs in an aerated medium. 3. Enzyme inactivation is mimicked in part by oxic incubation in an acidified medium containing 5,5-dimethyloxazolidine-2,4-dione, and by the action of calcium ionophore A23187. 4. Incubation of supernatant of gill homogenate results in a slow inactivation of pyruvate kinase that is inhibited by trifluoperazine or EGTA and stimulated by exogenous calmodulin. 5. Addition of ATP plus cAMP stimulates pyruvate kinase inactivation in supernatant of homogenized muscle but not so in a high molecular weight fraction thereof.

Pyruvate kinase of sea bass liver: interrelationship in regulating properties

Pyruvate kinase of sea bass liver show a joint modulation of both pH and temperature for PEP substrate. The effect of F-1,6-P2, alanine and ATP is not fundamentally affected by a variation in pH. The kinetic constants in the presence of ATP are not affected, but the intensity of its inhibitor effect varies with temperature. A study of different buffers: Tris-HC1, Tris-maleic and phosphate, on this enzymatic activity with or without effectors has been made.

Purification and properties of aerobic and anoxic forms of pyruvate kinase from red muscle tissue of the channelled whelk, Busycotypus canaliculatum

Aerobic and anoxic variants of radular retractor muscle pyruvate kinase (PK-aerobic and Pk-anoxic) from the gastropod mollusc, Busycotypus canaliculatum, were purified to homogeneity and respective specific activities of 368 and 186 mumol of product min-1 mg protein-1. Both PK variants were apparent homotetramers with native molecular masses of about 235 kDa, but differed in several other physical characteristics including pI (5.81 +/- 0.06 for PK-aerobic, 5.42 +/- 0.03 for PK-anoxic) and chromatographic behavior on several columns used during their respective purifications. The two enzymes differed greatly in several kinetic properties. Affinity for phosphoenolpyruvate was more than tenfold greater for PK-aerobic (K0.5 = 0.067 +/- 0.002 mM; h = 0.99 +/- 0.10), whereas the cooperative effect for phosphoenolpyruvate binding was greatly enhanced for PK-anoxic (K0.5 = 0.85 +/- 0.02 mM, h = 2.57 +/- 0.01). Although the affinities for the second substrate, ADP, were identical for both enzyme forms (apparent Km = 0.25 mM) pK-anoxic showed greater substrate inhibition by high concentrations of ADP. Likewise, affinities for K+ and Mg2+ were similar but PK-anoxic showed a greater degree of cooperativity with Mg2+ (h = 2.50 +/- 0.02) than did PK-aerobic (h = 1.70 +/- 0.06). Saturating concentrations of fructose 1,6-bisphosphate (50 microM) activated PK-anoxic resulting in an enzyme with properties similar to fructose-1,6-bisphosphate-activated PK-aerobic, with K0.5 values for phosphoenolpyruvate of about 0.04 mM and Hill coefficients of 1.1. PK-anoxic showed much stronger regulation by the allosteric inhibitors MgATP, phenylalanine, proline and alanine. Fructose 1,6-bisphosphate partially relieved the inhibitions by ADP, MgATP, alanine, proline and arginine phosphate of both enzyme forms. However, at 0.1 mM phosphoenolpyruvate PK-aerobic was much more sensitive to activation by fructose 1,6-bisphosphate, Ka values being 0.05 +/- 0.01 microM for PK-aerobic and 1.3 +/- 0.1 microM for PK-anoxic. In the presence of 1.0 mM alanine and 1.5 mM MgATP much higher concentrations of fructose 1,6-bisphosphate were required for activation of PK-anoxic (Ka = 5.2 +/- 0.4 microM) than for PK-aerobic (Ka = 0.02 +/- 0.01 microM). Variations in pH over the range likely occurring in vivo during anaerobiosis caused no significant additional kinetic differences between the two enzyme forms. The dissimilarity in kinetic properties of PK-aerobic and PK-anoxic indicate that red muscle PK activity is probably strongly depressed in vivo during anoxia stress.