Fructose 1,6-diphosphate and 3',5'-cyclic AMP as positive effectors of pyruvate kinase in developing embryos

Regulation of liver sea bass pyruvate kinase by temperature, substrates and some metabolic effectors

Pyruvate kinase of sea bass (Dicentrarchus labrax L.) shows positive cooperativity with respect to both substrates PEP and ADP. The temperature is a modulator of this activity, changing KS0.5 and Hill coefficient values for PEP. The enzyme shows alanine and ATP inhibition and F-1,6-P2 activation at 22 degrees C. F-1,6-P2 eliminates the effect of alanine but not that of ATP. These results could indicate a regulation of this enzyme by temperature and possess kinetic properties which are similar to that of L-type mammals.

Pyruvate kinases of salmon: purification and comparison with the isozymes from birds and mammals

Pyruvate kinase occurs as two major forms in coho salmon; the type M isozyme occurs primarily in muscle and heart, but type K has a more generalized tissue distribution, in parallel with the type K isozyme in other vertebrate systems. In order to assess the evolutionary relationships among the fish, avian, and mammalian isozymes of pyruvate kinase, we have purified the two isozymes from fish, have examined some of their physical properties, and have studied their immunological relationships to the avian and mammalian isozymes. Salmon type K is at least partially inactivated by antibody to bivine type L pyruvate kinase as well as by antibodies produced against chicken, bovine, and salmon type M isozymes. Salmon type M pyruvate kinase, on the other hand, is not significantly corss-reactive with the bovine type L isozyme, but is at least partially inactivated by antibodies produced against bovine or chicken type M isozymes. Mammalian type L pyruvate kinase is immunologically distinct from either mammalian type K or type M, but salmon type K has some structural features in common with all three mammalian isozymes. Thus, salmon fish type K pyruvate kinase could be similar to a primordial form that was antecedent to the three major differentiated isozymes of higher vertebrates.

Developmental changes in the pyruvate kinase isozymes of coho salmon

Pyruvate kinase exists as two major isozymes in coho salmon. As in mammals and birds, one form is present in the early embryo and maintains a wide tissue distribution in adults. This salmonid type K shows anodal migration during electrophoresis at pH 7.5. The appearence of functional musculature in the developing embryos. In adult animals this second form is the only pyruvate kinase in muscle. Brain, kidney, liver and gill contain primarily the type K pyruvate kinase while heart contains both major forms along with three intermediate forms which presumably constitute a hybrid set. Since there is no additional isozyme restricted to gluconeogenic tissues, we conclude that a type L isozyme has not developed in these animals. The two major isozymes are immunologically distincy. Both forms are dubject to fructose 1,6-bisphosphate activation of phosphoenolpyruvate binding, but the magnitude of the effect is small. The affinities for phosphoenolpyruvate are similar, but salmon type K has hyperbolic saturation curves with this substrate and type M has sigmoidal saturation curves. While the immunological data indicates considerable divergence in structure, the kinetic parameters of the two forms have remained relatively similar.

Secondary kinase reactions catalyzed by yeast pyruvate kinase

1. Yeast pyruvate kinase (EC 2.7.1.40) catalyzes, in addition to the primary, physiologically important reaction, three secondary kinase reactions, the ATP-dependent phosphorylations of fluoride (fluorokinase), hydroxylamine (hydroxylamine kinase) and glycolate (glycolate kinase). 2. These reactions are accelerated by fructose-1,6-bisphosphate, the allosteric activator of the primary reaction. Wth Mg2+ as the required divalent cation, none of these reactions are observed in the absence of fructose-biphosphate. With Mn2+, fructose-bisphosphate is required for the glycolate kinase reaction, but merely stimulates the other reactions. 3. The effect of other divalent cations and pH on three secondary kinase reactions was also examined. 4. Results are compared with those obtained from muscle pyruvate kinase and the implications of the results for the mechanism of the yeast enzyme are discussed.

A comparison of the properties of the pyruvate kinases of the fat body and flight muscle of the adult male desert locust

1. The pyruvate kinases of the desert locust fat body and flight muscle were partially purified by ammonium sulphate fractionation. 2. The fat-body enzyme is allosterically activated by very low (1mum) concentrations of fructose 1,6-diphosphate, whereas the flight-muscle enzyme is unaffected by this metabolite at physiological pH. 3. Flight-muscle pyruvate kinase is activated by preincubation at 25 degrees for 5min., whereas the fat-body enzyme is unaffected by such treatment. 4. Both enzymes require 1-2mm-ADP for maximal activity and are inhibited at higher concentrations. With the fat-body enzyme inhibition by ADP is prevented by the presence of fructose 1,6-diphosphate. 5. Both enzymes are inhibited by ATP, half-maximal inhibition occurring at about 5mm-ATP. With the fat-body enzyme ATP inhibition can be reversed by fructose 1,6-diphosphate. 6. The fat-body enzyme exhibits maximal activity at about pH7.2 and the activity decreases rapidly above this pH. This inactivation at high pH is not observed in the presence of fructose 1,6-diphosphate, i.e. maximum stimulating effects of fructose 1,6-diphosphate are observed at high pH. The flight-muscle enzyme exhibits two optima, one at about pH7.2 as with the fat-body enzyme and the other at about pH8.5. Stimulation of the enzyme activity by fructose 1,6-diphosphate was observed at pH8.5 and above.