Erythrocyte membrane vesicles and irreversibly sickled cells bind protein S

✍ Scribed by Dr. Peter A. Lane; Jacquie L O'Connell; Richard A. Marlar

• Publisher: John Wiley and Sons
• Year: 1994
• Tongue: English
• Weight: 635 KB
• Volume: 47
• Category: Article
• ISSN: 0361-8609
• DOI: 10.1002/ajh.2830470409

✦ Synopsis

Abstract

Plasma levels of free protein S, a vitamin K‐dependent anticoagulant, are decreased in persons with sickle cell anemia, but the etiology of the low levels is unknown. Protein S binds to phosphatidylserine‐containing phospholipids in a calcium‐dependent manner. Other studies have indicated that phosphatidylserine may be abnormally present on the outer surface of the membrane lipid bilayer of sickle cells and of the spectrin‐depleted vesicles they shed in vivo. We studied the binding of purified, radiolabeled protein S to spectrin‐depleted erythrocyte membrane vesicles and to density‐separated fractions of sickle and normal erythrocytes. Calcium‐dependent binding of protein S occurred with vesicles and with well‐aerated dense irreversibly sickled cells, but not with well‐aerated sickle discocytes or with normal erythrocytes. These data provide further evidence that phosphatidylserine is abnormally present on the outer surface of spectrin‐depleted vesicles and of irreversibly sickled cells. In addition, protein S binding to such sickle membranes in vivo may be responsible, in part, for the decreased levels of free protein S in sickle cell plasma. © 1994 Wiley‐Liss, Inc.