Properties of γ‐glutamyltransferase in developing brain

Cultures of smooth muscle cells and of fibroblasts from the rat aorta were tested for the capacity to synthesize and secrete nerve growth factor (NGF). Serum-free conditioned medium from both cell culture types contained NGF detectable by a dissociated sympathetic ganglion bioassay, a competitive receptor binding assay, and a non-competitive two-site radioimmunoassay. NGF synthesis was further demonstrated by the observation that smooth muscle cells incorporated 3H-labeled amino acids into protein which was speoifically precipitated by anti-NGF antiserum. Gel filtration chromatography of dialyzed and concentrated conditioned medium revealed that most of the NGF biological and antigenic activity was associated with a species having a molecular weight greater than 80,000° Medium conditioned by aortic smooth muscle cells contained, in addition to NGF, nondialyzable material which inhibited the bioassay response to NGF and material which enhanced the bioassay response to NGF.