From owner-metabolic-reg@net.bio.net Mon Feb 10 22:00:00 1997 Path: biosci!trop.ucl.ac.be!michels From: michels@trop.ucl.ac.be (Paul Michels) Newsgroups: bionet.metabolic-reg Subject: Re: Inorganic phosphate in plants Date: 11 Feb 1997 08:59:38 -0800 Organization: BIOSCI International Newsgroups for Molecular Biology Lines: 51 Sender: daemon@net.bio.net Distribution: world Message-ID: NNTP-Posting-Host: net.bio.net In reply to the question by Athel Cornish-Bowden on PPi metabolism in plants: PPi-dependent PFK and PPDK (pyruvate orthophosphate dikinase) seem to be present in the cytosol of many plants (co-existent with ATP-PFK and pyruvate kinase) It has been hypothesized that in plants and phototrophic protists a (Fru-2,6-P2 sensitive) PPi-PFK plays a role in (the forward direction) when oxygen levels are low and in other situations where the ATP/ADP ratio may be lowered (for a short review, see Mertens, E., FEBS Lett., 1991, 285, 1-5. PPDK is responsible for PEP formation in leaves of C4 plants. In these plants, PEP serves as the site of CO2 fixation during photosynthesis. Therefore, PPDK is under strict light/dark control. A reference: Edwards et al, Annu Rev. Plant Physiol. 1985, 36, 255- Paul Michels >My question is stimulated by David's comment, though it may not be >directly relevant to it. Does anyone know to what extent it is true (as >I was told a long time ago) that in plants inorganic phosphate fulfils >the role associated with ATP in animals, i.e. that phosphorylation of >many molecules is coupled to conversion of PPi to Pi rather than >conversion of ATP to ADP? If this is true, > >1. Are there parallel (alternative) ATP-using and PPi-using enzymes? > >2. Or are many of the usual ATP-dependent enzymes missing from plants? > >3. If alternative enzymes exist, how do they affect energy regulation, >and do they permit the sort of response to loss of ATP production that >David refers to above? > >4. References to reviews? > >Athel > >Home page: http://ir2lcb.cnrs-mrs.fr/lcbpage/athel/home_page.html >MCA FAQ: http://ir2lcb.cnrs-mrs.fr/lcbpage/athel/mcafaq.html >MCA chapter from my book: >http://ir2lcb.cnrs-mrs.fr/lcbpage/athel/fek10/mcai.html Paul Michels Research Unit for Tropical Diseases (TROP). International Institute of Cellular and Molecular Pathology (ICP). Avenue Hippocrate 74, B-1200 Brussels, Belgium. tel: +32-2-764.74.73 / 764.74.39 (secr); fax: +32-2-762.68.53 e-mail: michels@trop.ucl.ac.be .