Characterization of pituitary calcium-activated, phospholipid-dependent protein kinase: redistribution by gonadotropin-releasing hormone.
We report the presence in the rat pituitary of a calcium-activated, phospholipid-dependent protein kinase (C kinase), originally described by Takai et al. [Takai, Y., Kishimoto, A., Iwasa, Y., Kawahara, Y., Mori, T. & Nishizuka, Y. (1979) J. Biol. Chem. 254, 3692-3695]. Enzyme activity is absolutely dependent on the simultaneous presence of Ca2+ and phospholipid--in particular, phosphatidylserine. The presence of small amounts of unsaturated diacylglycerol greatly increases the apparent affinity of the enzyme for Ca2+ and phosphatidylserine. Pituitary C kinase is mostly soluble (70%) and partly particulate (30%). Although the soluble form of the enzyme can be detected in a crude cytosol preparation, the particulate form is detectable only after solubilization and anion-exchange chromatography. Administration of a gonadotropin-releasing hormone (Gn-RH) agonist analog, [D-Ser(But)6]des-Gly10-Gn-RH-N-ethylamide, to ovariectomized rats resulted in elevated serum luteinizing hormone levels (245%) accompanied by a decrease in the cytosolic form of the enzyme (60%) and an increase in the particulate form (300%) after 5 min. This apparent activation of the particulate form seems to result from translocation of a soluble C kinase to the membrane. Several endogenous substrate proteins for C kinase ranging from 16 to 100 kDa were identified in pituitary cytosol. Pituitary C kinase might be involved in signal-transduction mechanisms in Gn-RH action, in particular, and in other hypophysiotropic hormones, in general, which operate by means of stimulation of phosphoinositide turnover during which diacylglycerol is liberated.
D000818:Animals; D002451:Cell Compartmentation / Q000187:drug effects; D002462:Cell Membrane / Q000201:enzymology; D003600:Cytosol / Q000201:enzymology; D004789:Enzyme Activation; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D008970:Molecular Weight; D010743:Phospholipids / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism; D010902:Pituitary Gland / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism*; D011494:Protein Kinases / Q000378:metabolism; D051381:Rats
D010743:Phospholipids; D010750:Phosphoproteins; D007987:Gonadotropin-Releasing Hormone; D011494:Protein Kinases; D011493:Protein Kinase C