Changes in phosphatidylinositol phospholipase C isoenzymes and in their association with GTP gamma S-binding activity in guinea pig uterine smooth muscle during pregnancy.

Abstract

The nature distribution and associated GTP gamma S binding activity of phosphatidylinositol phospholipase C (PI-PLC) has been studied in non-pregnant and pregnant guinea pig uterine smooth muscle. Cytosolic fractions partially purified by Q-Sepharose and heparin-Agarose chromatography show two isoenzyme forms, one with an apparent molecular weight of 58 kD that crossreacts with PI-PLC alpha and a has Km for phosphatidylinositol of 292 +/- 72.6 microM, designated alpha, and a form that has an apparent molecular weight of 86 kD and a substrate Km of 54 +/- 20 microM designated delta. Approximately 80% of the total PI-PLC activity was recovered in the cytosolic fraction and this increased 8-10 fold for both isoenzymes from the non-pregnant to the late pregnant uterus and the proportion of the alpha isoenzyme increased from approximately 40% to 55% of the total. PI-PLC alpha but not delta activity had GTP gamma S binding activity associated with it after Q-Sepharose or heparin-Agarose chromatography. This associated activity accounted for 2% of the total GTP gamma S-binding activity in the non-pregnant uterus and 31% of that in the near-term uterus. On separation of the PI-PLCa-GTP gamma S-binding complex by gel filtration on Sephacryl S200 gave two peaks one of 118 kD accounting for two-thirds of all the binding and two-thirds of the enzyme activity and a 58 kD peak. The 118 kD peak could not be separated by treatment with 0.5% cholate, but in this form enzyme activity was protected from detergent inactivation found with the 58 kD form. In sodium dodecyl sulphate polyacrylamide-gel electrophoresis PI-PLC alpha was released from the 118 kD complex and showed an apparent molecular weight of 61.5 kD. All the activity in the residual membrane fraction could be released by washing with buffer followed by, 2 M KCl and then 2 M KCl plus 0.5% cholate. This released isoenzyme forms that appeared identical to those in the cytosolic fraction and with GTP gamma S-binding activity associated with PI-PLC alpha. It is concluded that in the near term guinea pig uterus there is a dramatic increase in the capacity for inositol polyphosphate production. Moreover the dramatic increase in GTP gamma S-binding activity associated with PI-PLC alpha implies large changes in the extent and possibly nature of the putative G-protein activation of this pathway.(ABSTRACT TRUNCATED AT 400 WORDS)