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W Merlevede

Publications and source records attributed to W Merlevede.

13 recordsLinked to original sources
PubMed1979

Liver phosphorylase b kinase. Cyclic-AMP-mediated activation and properties of the partially purified rat-liver enzyme.

Phosphorylase b kinase was extensively purified from rat liver. It was located in a form which could be activated 20--30-fold by a preincubation with adenosine 3':5'-monophosphate (cyclic AMP) and ATP-Mg. This activation was time-dependent, and was paralleled by a simultaneous incorporation of 32P from [gamma-32P]ATP into two polypeptides which comigrated in sodium dodecyl sulfate gel electrophoresis with the alpha and beta subunits of rabbit skeletal muscle phosphorylase b kinase. The liver enzyme was eluted from Sepharose 4B and Bio-Gel A-50m columns at the same place as muscle phosphorylase b kinase, which is indicative of a molecular weight of 1.3 x 10(6). After activation, the most purified liver preparation had a specific activity about 10-fold less than the homogeneous muscle enzyme at pH 8.2. The inactive enzyme form had a pronounced pH optimum around pH 6.0, whereas the activated form was mostly active above neutral pH. The activation of the enzyme reduced the Km for its substrate phosphorylase b severalfold. Liver phosphorylase b kinase was shown to be partially dependent on Ca2+ ions for its activity: addition of 0.5 mM [ethylenebis-(oxoethylenenitrilo)]tetraacetic acid (EGTA) to the phosphorylase b kinase assay increased the Km for phosphorylase b about twofold for both the inactive and the activated form of liver phosphorylase b kinase, but affected the V of the inactive species only.

Animals↗
PubMed1977

Multiple molecular forms of phosphorylase phosphatase associated with particulate glycogen and extracted from the cytosol of dog liver.

The glycogen pellet of dog liver extracts contains a phosphorylase phosphatase which has characteristics different from those of the phosphatases extracted from the cytosol. The phosphatase associated with glycogen is characterized by a M, of 51,000, a half maximal inhibition at 0.3 mM ATP (Hill coefficient : 2) and a Ki for Mg2+ of 1 mM. Treatment with urea or mercaptoethanol of the phosphatase associated with glycogen does not influence the activity, the Mr or the half maximal inhibition by ATP, but a decrease of the Hill coefficient for ATP is observed. A similar treatment of the phosphatases extracted from the high speed supernatant results in a decrease of the Mr of the spontaneously active form from 215,000 to 43,000, without an effect on the Ki for ATP (7 micronM), but accompanied by an increase in activity. The ATP-Mg dependent form of the phosphatase from the high speed supernatant (Mr : 138,000 ; Ka for ATP in the presence of 0.1 mM Mg2+ : 0.3 micronM), is denatured by urea or mercaptoethanol. The phosphatase associated with particulate glycogen cannot be found in the supernatant, nor the phosphorylase phosphatases present in the supernatant in the glycogen pellet. When all the glycogen is mobilized (starvation, glucagon) the phosphatase specifically associated with glycogen cannot be found as such in the cytosol. No activation of synthase beta can be detected neither with the phosphatases extracted from the cytosol nor with the enzyme released from the glycogen pellet.

Adenosine Triphosphate↗
PubMed1977

Effect of Mg2, ATP and some analogs on phosphorylase phosphatase from adrenal cortex.

The effect of Mg2, ATP and some of its analogs was studied on the spontaneously active and the ATP-Mg-dependent forms of phosphorylase phosphatase extracted from adrenal cortex. Inhibition of the spontaneously active form was observed with Mg2 (Ki - 9mM), ATP (Ki = 9micronM), 2'-doxy-ATP (Ki = 8 micronM), AtetraP (Ki = 9 micronM), AMP(CH2)PP (Ki = 11 micronM), ADP(CH2)P (Ki = 19 micronM), ADP(NH)P (Ki = 16micronM) and ADP (Ki = 25micronM). Activation of the ATP-Mg-dependent form was obtained with Mg2 (Ka = 0.55mM) (to a lower extent) and with ATP (Ka = 2micronM), 2'-deoxy-ATP (Ka = 6micronM) or AtetraP (Ka = 15micronM) in the presence of 0.5mM Mg2. Activation with AMP(CH2)PP was only observed in the presence of high concentrations (5mM) of Mg2 (Ka = 13micronM). No activation at all was observed with ADP(CH2)P or ADP(NH)P. Even though the activation of the ATP-Mg-dependent form does not seem to involve a kinase reaction, the stimulation by ATP or its analogs is rather specific, since it does not occur with analogs in which a methylene group or a nitrogen is substituted for the oxygen between the beta- and gamma-phosphates.

Adenosine Diphosphate↗