INIBIOLP   05426
INSTITUTO DE INVESTIGACIONES BIOQUIMICAS DE LA PLATA "PROF. DR. RODOLFO R. BRENNER"
Unidad Ejecutora - UE
artículos
Título:
Macrobrachium borellii hepatopancreas contains a single glycerol-3-P acyltransferase wich is located solely in mitochondria.
Autor/es:
PELLON-MAISON M; GARCIA CF; CATTÁNEO ER; COLEMAN RA; GONZALEZ-BARO MR
Revista:
LIPIDS
Editorial:
AOCS Press
Referencias:
Año: 2008
ISSN:
0024-4201
Resumen:
TRABAJO EN REVISIÓN. Mammals contain four isoforms of glycerol-3-phosphate acyltransferase (GPAT, EC 2.3.1.15).  GPAT1 and 2 are located on the outer mitochondrial membrane and GPAT 3 and 4 are in the endoplasmic reticulum (ER).  Although ER-GPAT isoforms account for the highest specific activity in mammalian tissues, GPAT1 may have been the first-appearing acyltransferase in evolution.  In E. coli and other bacteria, the only protein that expresses GPAT activity is plsB, a protein that has a 30% amino acid identity to rat GPAT1 and a similar molecular mass of ~ 70 kDa.       The hepatopancreas of the crustacean Macrobrachium borellii is an organ with functions analogous to both mammalian liver and adipose tissue; it has a high capacity for TAG biosynthesis, and its TAG stores are 80% of total lipids.  In order to understand the mechanism of glycerolipid biosynthesis in M. borellii, we investigated its hepatopancreas GPAT activity.  In hepatopancreas mitochondria, we identified a GPAT activity similar to that of mammalian GPAT1.  The activity was resistant to inactivation by SH-reactive N-ethylmaleimide, it was activated by polymyxin-B, and its preferred substrate was palmitoyl-CoA.  The reaction products were similar to those of mammalian GPAT1.  A 70-kDa protein band immunoreacted with an anti-rat liver GPAT1 antibody. Surprisingly, we did not detect high GPAT specific activity in hepatopancreas microsomes.  The amount of GPAT activity in microsomes was consistent with mitochondrial contamination, and the properties were similar to that of the mitochondrial activity.  TAG synthesis in microsomes was not dependent on the presence of glycerol-3 phosphate as a substrate, and the presence of lower Mg2+ and higher dithiothreitol concentrations in the reaction mixture altered the reaction products to diacylglycerols and decreased the extent of esterification of palmitate into glycerolipids.  We conclude that in the crustacean M. borellii the first step in the de novo glycerolipid biosynthetic pathway is carried out exclusively in mitochondria and the entire pathway can be completed in the mitochondria.  In contrast, TAG synthesis in the ER may function via the monoacylglycerol pathway.