DIFFERENTIAL-EFFECTS OF GLYCERO-PHOSPHOLIPOLYSIS AND SPHINGO-PHOSPHOLIPOLYSIS ON HUMAN HIGH-DENSITY-LIPOPROTEIN FLUIDITY

This study investigates the effect of enzymatic modifications of the H DL(3) surface lipid composition on their physical properties. Human HD L(3) (d: 1.125-1.21 g/ml) was treated either by an exogenous phospholi pase A(2) from Crotalus adamanteus or by a sphingomyelinase from Staph ylococcus aureus in the presence of albumin for various periods of tim e in order to obtain several degrees of hydrolysis. Glycerophospholipi d hydrolysis ranged from 13 to 81% and sphingomyelinase action led to a 31-92% sphingophospholipid degradation. Physical properties of the s urface of HDL(3) were examined by two spectroscopic methods: fluoresce nce polarisation and electron spin resonance. Glycerophospholipolysis treatment of HDL(3) enhanced the fluorescence anisotropy values (6-18% ) and both relaxation correlation time (30-100%) and degree of order, All these results indicated a more rigid environment, a decreased mobi lity and an increased order of the surface lipids. Conversely, treatme nt of the HDL(3) with sphingophospholipase induced a progressive fluid ization: fluorescence polarisation and degree of order decreasing down to 10% and relaxation correlation time down to 35% compared to native HDL(3), Taken together, all these observations suggest the relative i mportance of the two major phospholipids to modulate the fluidity and order of the surface of HDL(3) and could account for several recent ph ysiological observations.