Assembly and processing of procollagen type III in chick embryo blood vessels.

The processing of ['Hlproline-labeled procollagen 111 in excised chick embryo blood vessels was found to differ significantly from that of procollagen I in the same tissue.While first the amino propeptides and then the carboxyl propeptides were fairly rapidly cleaved from procollagen I, only the carboxyl propeptides were split off procollagen 111, leaving pN-collagen 111.This intermediate, which is only slowly converted to collagen 111 by loss of amino propeptides, was characterized by its sedimentation properties, isolation of the amino propeptide, and reaction with purified antibodies that are specific against bovine amino propeptide 111.It is interchain disulfide-linked, both through the amino propeptide and the carboxyl ends of the collagen chains.The conversion of procollagen 111 to pN-collagen 111 either in blood vessels, or after isolation by a carboxyl procollagen peptidase obtained from chick tendon fibroblast cultures, is inhibited by 50 m M arginine.Underhydroxylated procollagen 111 was isolated from blood vessels treated with a,a'-dipyridyl.Its amino propeptides reacted with the above antibodies but were not linked to each other.In contrast, its carboxyl propeptides were interchain disulfide-bridged, supporting previous suggestions that the carboxyl propeptides play a role in the assembly of procollagen trimer.Previous studies (1) with chick embryo blood vessels demonstrated that both types I and I11 collagenous proteins are synthesized during in vitro incubation.During a 1-h incubation period, type I procollagen' is processed to collagen, but type 111 procollagen is converted to only an intermediate precursor molecule which was assumed to be pN-collagen 111.In this paper, this intermediate is identified as pN-collagen 111, and a time course of its appearance and gradual conversion to collagen 111 is given.From various tissues, type 111 procollagen, pN-collagen, and collagen have been isolated (2-9).The type I11 amino propeptide derived from calf skin pN-collagen has been characterized and this propeptide has three domains (10, 11): a distal compact peptide, a short stretch of a collagen helix, and a short