Rapid turnover of phosphatidylinositol 3-phosphate in the green alga Chlamydomonas eugametos: signs of a phosphatidylinositide 3-kinase signalling pathway in lower plants?

• Published in: Biochemical journal Vol. 298; no. 2; pp. 269 - 273
• Main Authors: Munnik, T, Irvine, R.F, Musgrave, A
• Format: Journal Article
• Language: English
• Published: Colchester Portland Press 01.03.1994
• Subjects: Analytical, structural and metabolic biochemistry; Animals; Biological and medical sciences; Chlamydomonas - enzymology; Chlamydomonas eugametos; Freshwater; Fundamental and applied biological sciences. Psychology; Intermediary metabolites. Miscellaneous; kinases; Other biological molecules; phosphates; Phosphatidylinositol 3-Kinases; Phosphatidylinositol Phosphates - metabolism; phosphatidylinositols; Phosphatidylinositols - metabolism; Phospholipids - metabolism; Phosphorylation; Phosphotransferases (Alcohol Group Acceptor) - metabolism; Plants - enzymology; Plants - metabolism; Signal Transduction; Signal transduction; Phosphatidylinositol; Algae; Chlorophycophyta; Second messenger; Turnover; Lipids; Chlamydomonas; Thallophyta
• ISSN: 0264-6021; 1470-8728
• DOI: 10.1042/bj2980269

When Chlamydomonas eugametos gametes were incubated in carrier-free [32P]Pi, the label was rapidly incorporated into PtdInsP and PtdInsP2 and, after reaching a maximum within minutes, was chased out by recirculating unlabelled Pi in the cell. This pulse-chase labelling pattern reflects their rapid turnover. In contrast, incorporation into the structural lipids was slow and continued for hours. Of the radioactivity in the PtdInsP spot, 15% was in PtdIns3P and the rest in PtdIns4P, and of that in the PtdInsP2 spot, 1% was in PtdIns(3,4)P2 and the rest in PtdIns(4,5)P2, confirming the findings by Irvine, Letcher, Stephens and Musgrave [(1992) Biochem. J. 281, 269-266]. When cells were labelled with carrier-free both PtdInsP isomers incorporated label in a pulse-chase-type pattern, demonstrating for the first time in a plant or animal system that D-3 polyphosphoinositides turn over rapidly in non-stimulated cells, with kinetics similar to those shown by the D-4 isomers. In animal systems such lipids are already established as signalling molecules, and the data suggest that a similar role must be sought for them in lower plants such as Chlamydomonas.