PRODUCTION AND HYDROLYSIS OF CYCLIC ADP-RIBOSE AT THE OUTER SURFACE OF HUMAN ERYTHROCYTES

Hemoglobin-free membranes from human erythrocytes are able to convert β- NAD+ to cyclic ADP-ribose, a calcium mobilizer as potent as inositol 1, 4, 5- trisphosphate. Identification of cyclic ADP-ribose was based on HPLC analyses and its Ca2+-mobilizing activity on sea urchin egg microsomes. Erythrocyte membranes also hydrolyze cyclic ADP-ribose to ADP-ribose. By comparing the cyclic ADP-ribose-synthesizing and hydrolyzing activities on unsealed and right-side-out resealed ghosts, it can be concluded that both are localized at the extracellular side of the membrane. This is confirmed by the demonstration of both enzyme activities on the surface of intact human red cells. Identification of the two enzymes involved in cyclic ADP-ribose metabolism might suggest some physiological role of this nucleotide in red cells. © 1993 Academic Press, Inc.