Requirement of divalent cation for human platelet phosphorylase activity

Karpatkin, Simon; Braun, J.; Charmatz, Arthur

doi:10.1016/0005-2744(70)90225-1

Cited by 8 publications

(2 citation statements)

References 19 publications

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“…The activities of these isoenzymes were intermediate between those of phosphorylases b and a. Karpatkin et al (19,20) found that incubation of human platelets with MgATP+ resulted in an increase in total phosphorylase activity and concluded that the data were "consistent with the presence in human platelets of inactive dimer and monomer species of phosphorylase, which require MgATP for activation." Because activation of these isozymes was probably due to protein phosphorylation and also because incomplete phosphorylation could result in reduced activity, we evaluated the possibility that the activity of phosphorylase in McArdle muscle could be restored by phosphorylation of the inactive phosphorylase protein present in some patients.…”

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confidence: 52%

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Phosphorylation of McArdle phosphorylase induces activity.

Cerri¹,

Willner²

1981

Proc. Natl. Acad. Sci. U.S.A.

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In McArdle disease, myophosphorylase deficiency, enzyme activity is absent but the presence of an altered enzyme protein can frequently be demonstrated. We have found that phosphorylation of this protein in vitro can result in catalytic activity. We studied muscle of four patients; all lacked myophosphorylase activity, but myophosphorylase protein was demonstrated by immunodiffusion or gel electrophoresis. Incubation of muscle homogenate supernatants with cyclic AMP-dependent protein kinase and ATP resulted in phosphorylase activity. The activated enzyme comigrated with normal human myophosphorylase in gel electrophoresis. Incubation with [y-32P]ATP resulted in incorporation of 32P into the band possessing phosphorylase activity. Activation of phosphorylase by cyclic AMP-dependent protein kinase was inhibited by antibodies to normal human myophosphorylase or by inhibitory protein to cyclic AMP-dependent protein kinase. Incubation of muscle homogenates with phosphorylase b kinase and ATP also resulted in phosphorylase activity. After the action of cyclic AMP-dependent protein kinase, the resulting activity was similar to that ofphosphorylase b. However, incubation with phosphorylase kinase resulted in activity similar

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confidence: 52%

“…EDTA, peak II ofcAMP-Kase from bovine heart, phosphorylase b kinase, protein kinase inhibitor (from rabbit skeletal muscle), glycogen, 2-mercaptoethanol, Na (20). Protein was determined according to Lowry (26).…”

Section: Methodsmentioning

confidence: 99%

Phosphorylation of McArdle phosphorylase induces activity.

Cerri¹,

Willner²

1981

Proc. Natl. Acad. Sci. U.S.A.

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Platelet calcium‐dependent proteins: Identification and localization of the calcium‐dependent regulator, calmodulin, in platelets

1981

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The calcium-dependent regulator protein, calmodulin, is a 17,000 molecular weight polypeptide which binds calcium and has been shown to confer calcium sensitivity on contractile and other proteins. In the present study, we have examined the presence and subcellular distribution of this protein in preparations of human platelets. Calmodulin was quantified using a two-stage phosphodiesterase assay. Whole platelets contained 1.33 +/- 0.06 units calmodulin per 10(6) platelets or 26.5 +/- 3.4 fg calmodulin per platelet. The distribution of calmodulin in the platelet was predominantly soluble with over 80 percent of calmodulin activity in the soluble fraction of the cell. There was no apparent difference in the distribution of calmodulin between soluble and particulate compartments in recalcified platelet homogenates compared to homogenates in EDTA. Indirect immunofluorescent studies with monospecific antisera to dinitrophenylated calmodulin showed intense staining of platelets in a diffuse pattern. The identification of calmodulin in platelets raises the possibility that this protein may participate in calcium-dependent reactions important in platelet aggregation and release.

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