ADP-RIBOSYLATION OF MYELIN BASIC-PROTEIN AND INHIBITION OF PHOSPHOLIPID VESICLE AGGREGATION

Four isoforms of myelin basic protein (MBP) from chicken brain were AD P-ribosylated by chicken heterophil ADP-ribosyltransferase. The 21-kD isoform was the most preferential substrate of this transferase. With this isoform, the K-m values were estimated to be 330 mu mol/l for NAD and 30 mu mol/l for MBP, and the optimal pH for ADP-ribosylation was 8.5. The stoichiometry of ADP-ribose incorporation into 21-kD MBP was 3.5 mol of ADP-ribose/mol MBP. We found the inhibition of ADP-ribosyla tion of MBP by hydroxylamine and L-arginine indicating that this modif ication was likely to be mediated by arginine residues. Proteolytic pe ptide maps of ADP-ribosylated MBP by chicken ADP-ribosyltransferase an d cholera toxin showed partially different radio active bands. When 21 -kD MBP was ADP-ribosylated by chicken transferase, the potential for phospholipid vesicle aggregation was reduced in proportion of the degr ee of ADP-ribosylation. The possibility that ADP-ribosylation of MBP m ay control stabilization of myelin through regulation of its affinity for phospholipid in vivo would need to be considered.