Glycerol-3-phosphate acyltransferase activity subcellular localization

PELLON-MAISON, M.; COLEMAN, R.A.; GONZALEZ-BARO, M.R.

Pinamar, Bs As, Argentina

Congreso; XLI Reunion anual de SAIB (Sociedad Argentina de Investigacion Bioquimica y Biologia Molecular); 2005

SAIB

Two isoforms of glycerol-3-phosphate acyltransferase (GPAT) have been historically described in rat liver: a SH-group-reactive-substances (SGRS)-sensitive form located in the ER (mcGPAT) and a SGRS-resistant form, in the outer mitochondrial membrane (mtGPAT1). A second SGRS-sensitive form was recently described in mitochondria of nule-mtGPAT1 mice.  Rat liver was fractionated, microsomes (Mc) and crude mitochondria (cMt) obtained. Further purification of cMt yielded highly-purified mitochondria (pMt), and two fractions of mitochondria-associated membranes, MAM1 and MAM2. Glycerolipid synthesis capability was assessed by assaying total- and SGRS-resistant-GPAT activity. SGRS-sensitive GPAT activity was calculated differentially. The presence of mtGPAT1 was determined by western blot. SGRS-resistant-GPAT activity results, higher in pMt, were inconsistent with the presence of mtGPAT1, mainly in MAM1. Cross-contamination of the fractions was discarded by measuring marker enzymes activities and proteins. We postulate that i) mtGPAT1 cuold be found in two states: less-active in MAM1 and it would traslocate to mitochondria for activation, or ii) the existance of at least another isoform of SGRS-resistant GPAT that makes up for the activity in pMt.