The regulation of liver phosphoprotein phosphatase by inorganic pyrophosphate and cobalt

Khandelwal, Ramji L.

doi:10.1016/0003-9861(78)90418-6

Cited by 31 publications

(8 citation statements)

References 37 publications

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“…The inclusion of 0.25 M KC1 in the extraction buffer was necessary to achieve maxima< reco-+e+s of &F-2 a&Vity as previously reported [.221. The exfracfion medium contained BDTA t0 &da& Mg2+ ions and thus inhibit protein kinases and sodium pyrophosphate to inhibit protein phosphatases [23]. Fluoride ions were not used because MgFz is only sparingly soluble and eIF-2 assays contain Mg2+ ions.…”

Section: Isolation and Assay Of Eif-2 From Gastrocnemius Musclementioning

confidence: 99%

Regulation of polypeptide‐chain initiation in rat skeletal muscle Starvation does not alter the activity or phosphorylation state of initiation factor eIF‐2

Cox¹,

Redpath

Proud

1988

FEBS Letters

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In rats, 48-h starvation causes a decrease in the rate of protein synthesis in skeletal (e.g. gastrocnemius)muscle, due largely to impairment of peptide-chain initiation. In other cell types inhibition of initiation is associated with decreased activity and recycling of initiation factor eIF-2, and increased phosphorylation of its a-subunit. However, 48-h starvation has no effect on the activity or recycling of eIF-2 measured in extracts of gastrocnemius muscle, or on the level of a-subunit phosphorylation.The effects of starvation on peptide-chain initiation in skeletal muscle must therefore involve alterations in other components of the translational machinery.

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Section: Isolation and Assay Of Eif-2 From Gastrocnemius Musclementioning

confidence: 99%

Regulation of polypeptide‐chain initiation in rat skeletal muscle Starvation does not alter the activity or phosphorylation state of initiation factor eIF‐2

Cox¹,

Redpath

Proud

1988

FEBS Letters

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“…It is thus possible to explain away the reversal seen with Co injection as being due to Co competing with Mn at the active centre ofthe enzyme. Alternatively, Co could be inhibitory with respect to phosphatase when PPi is low, as reported by Khandelwal (1978). Insofar as Co is concerned, only one of the three fibres tested displayed a reversal.…”

Section: Reversal Of the Response To Gtp And Atp By Injecting Mgcl2mentioning

confidence: 92%

“…rabbit liver phosphatase (Khandelwal, 1978) and dog heart phosphatase (Hsiao, Sandberg & Li, 1978). Fig.…”

Section: E E Bittar and J Nwoga 504 Gtp On Musclementioning

confidence: 99%

Stimulation by injected guanosine triphosphate of the sodium efflux in barnacle muscle fibres pre‐exposed to aldosterone.

Bittar¹,

Nwoga²

1981

The Journal of Physiology

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SUMMARY1. A study has been made of the response of the Na efflux to injected guanosine triphosphate (GTP) in barnacle muscle fibres pre-exposed to aldosterone.2. (i) Injection of GTP into unpoisoned fibres causes a transitory stimulation. By contrast, injection ofGTP into ouabain-poisoned fibres causes a sustained stimulation. Little or no fall in Em is recorded following GTP injection.(ii) The stimulatory response to GTP of aldosterone pre-exposed ouabain-poisoned fibres differs from that seen in unexposed, ouabain-poisoned fibres, in that its magnitude is greater and always sustained.3. The magnitude of the response to GTP depends on external Ca and pH but not external Na. The response itself is not seen at 0 'C.4. (i) Verapamil reduces the size of the response to GTP only if applied before GTP. Injection of EGTA, Fe, Zn and Co partially abolishes the residual response.(ii) Injection of MgCl2 almost completely reverses the response to GTP. KCl is ineffective.5. These results are explained by supposing that removal of internal Mg and trace elements by GTP leads to activation of phosphoprotein phosphatase.

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“…How ever, the mechanism of cobalt activation is different. In the case of cardiac and liver enzyme, cobalt ions act directly on the cata lytic properties of the enzyme molecules [5,6]. Contrary to this, cobalt ions do not in fluence the catalytic properties of our E3 [2] and E2 ( fig.…”

Section: Methodsmentioning

confidence: 99%

“…While both molecular weight forms of E3 phosphatase (95,000 and 25,000 dal tons) dephosphorylated only protein sub strates (casein and spectrin but not phosvi tin) under neutral (pH 6.8) conditions [2], E2 phosphatase under neutral conditions m ent casein phosphatases in the cytosol of human cord blood erythrocytes whose activ ity is positively regulated by C0CI2 concen trations. Cobalt-dependent protein phospha tases have already been described in cardiac and skeletal muscle [5] and in liver [6]. How ever, the mechanism of cobalt activation is different.…”

Section: Methodsmentioning

confidence: 99%

Cobalt-Dependent Protein Phosphatases from Human Cord Blood Erythrocytes

Japundzić¹,

Levi²,

M³

1988

Enzyme

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Of three casein phosphatases isolated from the cytosol of human cord blood erythrocytes two were cobalt-dependent, E(2) and E(3). In the presence of C0CI(2), E(2) activity was the most prominent. In addition to casein, E(2) dephosphorylated phosvitin and p-nitrophenyl phosphate (p-NPP) with pH optima at Ó.8-7.2 for proteins and 9.0 for p-NPP. The native enzyme had a molecular weight of 104,000 daltons after AcA-44 Ultrogel filtration. According to SDS/PAGE it consisted of two subunits, 78,000 and 15,000 daltons. The 104,000- dalton form exhibited Michaelis-Menten kinetics and had the greatest affinity for casein between protein substrates tested. Ethanol denaturated the enzyme by 80%. Optimal activation of E(2) phosphatase was achieved with 5 mmol/1 CoCl(2) which did not affect the catalytic properties of the enzyme but did affect the rate of ‘E-S’ complex formation. Inorganic pyrophosphate was not inhibitory for the 104,000-dalton enzyme. Judging by all these properties the natural substrate for E(2) casein phosphatase could be P-pyruvate kinase.

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The regulation of liver phosphoprotein phosphatase by inorganic pyrophosphate and cobalt

Cited by 31 publications

References 37 publications

Regulation of polypeptide‐chain initiation in rat skeletal muscle Starvation does not alter the activity or phosphorylation state of initiation factor eIF‐2

Regulation of polypeptide‐chain initiation in rat skeletal muscle Starvation does not alter the activity or phosphorylation state of initiation factor eIF‐2

Stimulation by injected guanosine triphosphate of the sodium efflux in barnacle muscle fibres pre‐exposed to aldosterone.

Cobalt-Dependent Protein Phosphatases from Human Cord Blood Erythrocytes

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