ERYTHROCYTE LIPIDS IN TRIOSE-PHOSPHATE ISOMERASE DEFICIENCY

Marked hypoalphalipoproteinemia was found together with relatively low serum cholesterol, triacylglycerol, and LDL levels in a triose-phosph ate isomerase (TPI; D-glyceraldehye-3-phosphate ketol-isomerase, EC 53 .1.1)-deficient Hungarian family, especially in the two compound-heter ozygote brothers. Apart from a slight increase in palmitic and stearic acids together with a slight decrease in oleic and linoleic acids, no other changes were found in the fatty acid composition of the erythro cyte phospholipids. Anisotropy measurements with n-(9-anthroyloxy)stea ric and -palmitic acid fluorophores revealed increased motional freedo m of the fatty acid chains in the external lipid layers of the intact erythrocytes from all members of the TPI-deficient family as compared with normal age-matched controls. This asymmetric increase in membrane fluidity was found to be significantly higher in the propositus than in his compound-heterozygote brother without any neurological disorder s. The change in membrane fluidity may result from as-yet-unresolved a spects of the lipid composition of the plasma membrane. Our findings t hat the differences between the TPI-deficient individuals and normal c ontrols and the differences between the two compound-heterozygote brot hers were all absent in the phospholipid extracts of the same erythroc ytes favor the assumption that the increased motional freedom of the f atty acid chains in the external surface of the bilayer is caused by t he binding of the mutant TPI molecule to the N-terminal sequence of ba nd 3 protein.