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S D Yang

Publications and source records attributed to S D Yang.

108 records · Page 6Linked to original sources
PubMed1983

Role of the modulator protein in the interconversion of rabbit skeletal muscle protein phosphatase.

The major active protein phosphatase present in a rabbit skeletal muscle extract is associated with the glycogen particle and migrates in sucrose density gradient centrifugation as a Mr = 70,000 protein and contains modulator activity. Addition of extra modulator protein causes a time- and concentration-dependent conversion of the enzyme to an inactive FA-ATP, Mg-dependent form. The intrinsic modulator in the active phosphatase is destroyed by limited proteolysis without an appreciable change in the phosphatase activity. The proteolyzed active enzyme has a lower molecular weight (Mr = 40,000) and it reassociates with the modulator producing a FA-ATP, Mg-dependent enzyme form (Mr = 60,000). The modulator protein is used stoichiometrically in the activation of the ATP, Mg-dependent phosphatase. This is in agreement with the presence of one unit of modulator activity per unit of native spontaneously active phosphatase.

Adenosine Triphosphate↗
PubMed1983

The heat labile phosphatase modulator (inhibitor-2) complex from rabbit skeletal muscle.

The heat stable phosphatase modulator protein (inhibitor-2) has been shown to play a crucial role in the reversible ATP, Mg-dependent activation of a multisubstrate protein phosphatase. The modulator activity is acid and heat stable and resides in a small asymmetrical protein which, after boiling migrates in sucrose density gradient centrifugation with a molecular weight of 17K. The present report shows that in unboiled rabbit skeletal muscle preparations all the modulator activity is found associated with a heat labile protein component, which imposes an important regulatory feature on the heat stable activity. The heat labile complex migrates in sucrose density gradient centrifugation as a Mr = 70K protein.

Animals↗
PubMed1981

Identification of inhibitor-2 as the ATP-mg-dependent protein phosphatase modulator.

In previous reports (Yang, S. D., Vandenheede, J. R., Goris, J., and Merlevede, W. (1980) J. Biol. Chem. 255, 11759-11767; Vandenheede, J. R., Yang, S.-D., and Merlevede, W. (1981) J. Biol. Chem. 256, 5894-5900), we have described two slightly different purification procedures for the isolation of the inactive ATP-Mg-dependent protein phosphatase (FC) which could be activated by a protein activator (FA) in the presence of ATP-Mg. Although the two procedures consistently produced FC preparations that showed very similar polyacrylamide gel patterns, the specific activity of the purified enzymes varied considerably. The preparations characterized by a rather low specific activity could be stimulated up to 10-fold when a titrated amount of inhibitor-2 was included during the FA and ATP-Mg-mediated activation. Inhibitor-2, only recently implicated as an inactivating protein for activated FC (Vandenheede, J. R., Goris, J., Yang, S.-D., Camps, T., and Merlevede, W. (1981) FEBS Lett. 127, 1-3) has now been identified as a modulator protein, necessary for the reversible activation of the protein phosphatase.

Adenosine Triphosphate↗
PubMed1980

ATP x Mg-dependent protein phosphatase from rabbit skeletal muscle. I. Purification of the enzyme and its regulation by the interaction with an activating protein factor.

An ATP x Mg-dependent protein phosphatase (FC) was purified to near homogeneity from rabbit muscle. The enzyme was completely devoid of any spontaneous activity but could be activated by a protein activator (FA) in the presence of ATP and Mg ions. The inactive phosphatase migrated as a single protein band on sodium dodecyl sulfate-gel electrophoresis, and in discontinuous gel electrophoresis, where the potential phosphatase activity was located in the main protein band. The molecular weight determined by sodium dodecyl sulfate electrophoresis or by sucrose density centrifugation was found to be 70,000. FC migrated on gel filtration as a 140,000 molecular weight species. The activation by FA was not paralleled by an incorporation of [32P]-phosphate into the ATP x Mg-dependent phosphatase, and from the kinetics of activation a protein-protein interaction with ATP x Mg as a necessary factor, can be inferred as the mechanism of activation. After activation by FA and ATP X Mg, the purified enzyme had a specific activity of 10,000 units/mg of protein, and a Km for rabbit muscle phosphorylase a of approximately 1.0 mg/ml. The activated enzyme did not release [32P]phosphate from 32[-labeled rabbit muscle synthase b, prepared from glucagon-treated dogs. It did, however, remove all the 32P label from phosphorylase b kinase, autophosphorylated to the level of 2.0 mol/mol of 1.3 X 10(6) molecular weight.

Adenosine Triphosphate↗
PubMed1980

ATP x Mg-dependent protein phosphatase from rabbit skeletal muscle. II. Purification of the activating factor and its characterization as a bifunctional protein also displaying synthase kinase activity.

A protein (FA) has been isolated from rabbit muscle which has two functions: one is the activation of the ATP x Mg-dependent phosphatase (see previous paper) (1) and the second is the phosphorylation and concomitant inactivation of glycogen synthase, independent from cyclic AMP or Ca ions. The two activities co-purify throughout the purification scheme, and reside in the single protein band that the purified preparation shows in discontinuous acrylamide gel electrophoresis. Heat inactivation experiments with the purified protein showed a parallel decrease of both activities with time. GTP could efficiently replace the ATP in both reactions. Sodium dodecyl sulfate-gel electrophoresis also shows a single protein-stained band corresponding to a Mr = approximately 50,000 and sucrose density gradient centrifugation gave a value of 45,000. The enzyme incorporates only 1 mol of phosphate/mol of synthase monomer (85,000 daltons) and brings the activity ratio (+/- glucose-6-P) down to less than 0.05. Kinetic studies suggest that FA exerts its two activities in quite different ways: the activation of the ATP x Mg-dependent phosphatase is bought about by a protein-protein interaction (FA x FC complex formation) with ATP x Mg as a necessary cofactor, whereas for the inactivation of synthase, FA is a cyclic AMP- and Ca-independent kinase.

Adenosine Triphosphate↗
PubMedDate not supplied

Bioflavonoids commonly and potently induce tyrosine dephosphorylation/inactivation of oncogenic proline-directed protein kinase FA in human prostate carcinoma cells.

In this study, we investigate the effect of bioflavonoids on the activity and phosphotyrosine content of oncogenic proline-directed protein kinase FA (PDPK FA) in human prostate carcinoma cells. Chronic treatment of human prostate carcinoma cells with low concentrations of quercetin, apigenin, and kaempferol commonly and potently induced tyrosine dephosphorylation and concurrent inactivated oncogenic PDPK FA in a concentration-dependent manner. This is demonstrated by a specific assay of this kinase's activity in the immunoprecipitates from the cell extracts followed by immunoblotting and phosphotyrosine analysis. The results indicate that bioflavonoids may function as common tyrosine kinase inhibitors to inhibit PDPK FA-specific tyrosine kinase and thereby to induce tyrosine dephosphorylation/inactivation of this oncogenic kinase in human carcinoma cells. Under this condition, quercetin, apigenin, and kaempferol can also inhibit cell growth in a similar concentration-dependent manner. The results further indicate that inhibition of tyrosine phosphorylation/activation of this oncogenic PDPK represents a new mode of action mechanism for bioflavonoids during the antiproliferation process in human carcinoma cells.

Flavonoids↗