Partial characterization of guanylate cyclase activity of the human placenta

L. Milewich, T. S. Hendricks, N. F. Gant, B. E. Schwarz, P. C. MacDonald

Research output: Contribution to journalArticle

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Abstract

An optimal assay system for the measurement of GC activity in subcellular fractions of human placenta homogenates was developed. Mn2+ was more effective than Mg2+ as a cofactor and, in addition, it markedly potentiated the Mg2+ -dependent GC activity. The apparent optimal temperature for GC activity was 45°C and the pH optimum was in the range of 7.5 to 8.3. The apparent K of Mn2+ -dependent GC for GTP was 0.1 mM and that of Mg2+ -dependent GC for GTP was 0.4 mM. More than 95 per cent of GC activity was associated with the 100,000 x g supernatant fraction. ATP at a concentration of 0.5 mM inhibited GC activity by 50 per cent. The Mn2+ -dependent GC activity was inhibited by p-hydroxymercuriphenyl sulphonate at concentrations between 10 and 50 μM; this inhibition was reversed, in part, by dithiothreitol at concentrations of 150 to 500 μM to approximately one-fifth the activity of control values. In addition, we found that dithiothreitol was an inhibitor of GC activity. Studies on the responsiveness of placental GC to nucleophilic compounds indicated that phenylhydrazine was the most potent stimulus, while hydroxylamine, hydrazine, sodium azide, sodium nitrite and sodium nitroprusside were less potent. Placental GC was unaffected by α- and β-adrenergic agonists or by cholinergic agonist, as well as by steroids produced by the placenta.

Original languageEnglish (US)
Pages (from-to)343-354
Number of pages12
JournalPlacenta
Volume2
Issue number4
DOIs
StatePublished - 1981

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hydrazine
Guanylate Cyclase
Dithiothreitol
Guanosine Triphosphate
Human Activities
Placenta
Sodium Nitrite
Cholinergic Agonists
Sodium Azide
Adrenergic Agonists
Hydroxylamine
Subcellular Fractions
Nitroprusside
Adenosine Triphosphate
Steroids
Temperature
phenylhydrazine

ASJC Scopus subject areas

  • Obstetrics and Gynecology

Cite this

Partial characterization of guanylate cyclase activity of the human placenta. / Milewich, L.; Hendricks, T. S.; Gant, N. F.; Schwarz, B. E.; MacDonald, P. C.

In: Placenta, Vol. 2, No. 4, 1981, p. 343-354.

Research output: Contribution to journalArticle

Milewich, L. ; Hendricks, T. S. ; Gant, N. F. ; Schwarz, B. E. ; MacDonald, P. C. / Partial characterization of guanylate cyclase activity of the human placenta. In: Placenta. 1981 ; Vol. 2, No. 4. pp. 343-354.
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