THE INFLUENCE OF CALCIUM AND MAGNESIUM ON SEA BASS (DICENTRARCHUS-LABRAX) INTESTINAL BRUSH-BORDER MEMBRANE PURIFICATION AND ACTIVITY

1. The activity of brush border enzymes (alkaline phosphatase, maltase , sucrase, trehalase, leucine amino peptidase) was higher in purified membranes prepared with calcium. The contamination of these membranes with basolateral membranes was also lower (1.27 for Na-K-ATPase activi ty ratio). 2. The extraction of brush border lipids was carried out ac cording to Folch adapted method. Two dimensional thin layer chromatogr aphy was used to separate the phospholipidic fractions. Fatty acids of phospholipids were analysed using gas chromatography after acid trans methylation (column SP 2330). 3. Phospholipids are composed of phospha tidylcholine (PC: 33%), phosphatidylethanolamine (PE: 30%), sphingomye line (SM: 21%), phosphatidylserine (PS: 14%) and phosphatidylinositol (PI: 2%). 4. PC, PE and PS are characterized by high levels of unsatur ated fatty acids (monounsaturated MUFA: 21.5% and polyunsaturated PUFA : 34.9%). The most abundant PUFA belong to the (n-3) family [18:3 (n-3 ), 20:5 (n-3) and 22:6 (n-3)]. 5. Fatty acids from sphingomyelin of pu rified membranes have low proportions of PUFA (13.5%) but higher propo rtions of MUFA (39.5%). 6. No specific differences were found between calcium and magnesium prepared membranes. 7. The low content in LPC an d the absence of LPE confirmed the absence of major structural lipids transformation during the membrane purification with calcium or magnes ium. 8. Glycine transport was measured during 10 sec at different temp eratures using the rapid filtration technique. Glycine transport was h igher with Na+ than with K+. In the presence of Na+, this transport in creases with temperature. 9. Arrhenius curves were mono phasic without obvious breakpoint and indicated no phase transition in the lipid bil ayer. 10. A significant Na+ dependent glycine transport has been chara cterized at low temperatures (0-degrees-C) which suggests a possible r ole of membrane polyunsaturated fatty acids in the control of glycine transport.