ADP-RIBOSYLTRANSFERASE ACTIVITY IN MYELIN MEMBRANES ISOLATED FROM HUMAN BRAIN

An ADP-ribosyltransferase has been identified in compact myelin and in several white matter fractions which contain less compact myelin, fra ctionated on the basis of increasing protein/lipid ratios. One fractio n the P(3)A contained the greatest activity although the activity in c ompact myelin was only slightly less. The ADP-ribosyltransferase activ ity of solubilized myelin was stimulated by increasing amounts of GTP gamma S and was specific for the beta-isomer of NAD. Although ADP-ribo sylation was demonstrated with the heterotrimeric G proteins in the 40 -50 kDa range, the substrate for the ADP-ribosyltransferase in the 20 kDa range was identified as MBP.