Solubilization and some properties of gamma-glutamyltransferase from human brain microvessels

Detergents Triton X-100, sodium deoxycholate, and octyl-beta-D-glucopyranoside, and proteinase papain proved to be excellent agents solubilizing the gamma-glutamyltransferase (gamma-GT) from human brain cortex microvessels. Ficin also solubilized gamma-GT but to a lesser extent than papain. The relative molecular mass of the detergent-solubilized enzyme form was greater than 200,000 (in the presence of Triton X-100). The relative molecular mass of the proteinase-solubilized form was slightly greater than that of albumine. gamma-GTs of microvessels from five human brain regions and from the choroid plexus were tested for their specificity toward acceptors. The best acceptors were found to be (in decreasing order of activity) L-cystine, glycylglycine, L-glutamine, L-methionine, and L-alanine. The findings suggest that the main features of gamma-GT of the human blood-brain barrier are very similar to those of gamma-GTs from other human tissues.