Asymmetric metabolism of phosphatidylethanolamine in the human red cell membrane.

G.V Marinetti,K Cattieu

doi:10.1016/s0021-9258(19)68352-3

Abstract

The incorporation of labeled fatty acids into phosphatidylethanolamine (PE) on the two sides of the human red cell membrane was studied by use of the vectorial probe trinitrobenzene sulfonate (TNBS). A small population of PE molecules on the outer surface of the membrane has a 4-fold higher turnover rate than the remaining PE molecules. This effect is greatest with palmitic acid, less with linoleic and linolenic acids, and not seen with stearic acid. By use of the hydrophobic penetrating probe fluorodinitrobenzene (FDNB), we find a second larger population of PE and phosphatidylserine (PS) molecules which reacts with FDNB and has a higher specific activity than the PE and PS molecules which do not react. With human polymorphonuclear cells, the labeled PE molecules inside the cell have a higher specific activity than the PE molecules located on the outer cell surface. These results suggest that there are heterogeneous populations of PE and PS on both halves of the red cell membrane which show different metabolic turnover rates of their fatty acids.

Highlights

In order to furtherexplore the origin of the asymmetry of vectorialprobetrinitrobenzenesulfonate(TNBS)
A the red cell membrane, we have studied the incorporation of small population ofPE molecules on the outer surface differentfatty acids into the variousphospholipids of the of the membranehas a 4-fold higher turnovrearte than the remainingPE molecules.This effect is greatest with palmitic acid,less with linoleic and linolenicacids, and not seen with stearic acid
Do certain phospholipids have a different asymmetric metabolism and are therediscrete populations of phospholipids on either surface of the membrane which have a different turnover than other phospholipids of the same type? We studied this problem by labeling PE and PS in intact red cells with radioactive fatty acids and using vectorial probes to sense certain populations of PE and PS and analyzing their specifk activities

Summary

Asymmetric Metabolism of Phosphatidylethanolaminein the Human Red Cell Membrane*

From the Departmentof Biochemistry, University ofRochester Medical Center, Rochester, New York 14642. The labeled PE molecules inside the cell have a higher specific activity than the PE molecules located on the outer cell surface. Renooij et al (7, 8) reported that the incorporation of different fatty acids into PC of isolated rat red cells occurred predominantly on the inner layoefr the membrane. ACS grade chloroform, methanol,aceticacid,n-propyl alcohol, acetone,and propionic acid were obtained from Fisher Scientific The chloroform, They state thatwt o mechanisms may accounftor the renewal acetone, and methanol were distilled prior to use. The nonpermeable probe TNBS was used to measure the specific activity of PE andPS on the outer surfaceof the red nuclear; BSA,bovine serum albumin.

Phosphatidylethanolamine Turnover in Red Cells

Unreacted PE

DISCUSSION