Ribonucleoprotein complexes of pyruvate kinase from human skeletal muscle
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About 25% of total pyruvate kinase activity in muscle appears in a bound form which is insoluble in water or diluted salt solutions at pH 5.8. That activity is associated with the ribonuc-leoprotein complexes and is soluble at high ionic strength. A procedure is described for the purification and crystallization of this enzyme form herein called pyruvate kinase MB and water soluble form MA.
Crystalline nucleoproteins are composed of active and inactive RNA-protein complexes with varying RNA content. By fractional crystallization and gel filtration a number of crystalline complexes were separated, two of them highly purified. One preparation was homogenous, contained 0.5% RNA and had a specific activity of 265 U/mg protein, the other one 10% RNA and 200 U/mg protein respectively.
Forms MA and MB share the same protein as shown in immunodiffusion test with the anti-MA sera. They differ in solubility and stability in diluted solutions. In Tris-HCl buffer, pH 7.6 form MB is rapidly inactivated whereas form MA is quite stable under the same conditions. Both forms have different Km for phosphoenolpyruvate and ADP and Vmax as well.
Digestion of pyruvate kinase MB with RNase was without marked effect on specific activity of the enzyme.
The presence of numerous ribonucleoprotein complexes with a polynucleotide content in the range of 0.5 to 20% and specific activity of 160–220 U/mg protein suggests the control by RNA binding of pyruvate kinase activity from human skeletal muscle.
KeywordsFractional Crystallization Pyruvate Kinase Phosphoenolpyruvate Human Skeletal Muscle High Ionic Strength
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