SYNTHESIS AND SECRETION OF TRANSCOBALAMIN-II BY CULTURED ASTROCYTES DERIVED FROM HUMAN BRAIN-TISSUE

Astrocytes derived from human brain tissue secreted a single cobalamin (vitamin B-12, Cbl) binding protein over a 4 day period in culture. C ycloheximide reversibly inhibited the release, and the binding protein was identified as transcobalamin II (TCII) based on molecular size, r eaction with anti-human TCII antiserum, precipitation with 2.0 M ammon ium sulfate and its ability to bind radioactive cyanocobalamin. It als o enhanced the cellular incorporation of the vitamin. Our data show th at cultured cells from human brain synthesize and secrete TCII and sug gests that at least some of the TCII known to be present in cerebrospi nal fluid may originate from within the central nervous system.