Transferrin occurs in the vitreous at a higher relative concentration than found in the plasma or in the aqueous humor. This has been related to a possible local synthesis of transferrin by some component of the eye, although convincing evidence for this has not been available. Recently, the intraocular synthesis of several vitreous glycoproteins, possibly by the ciliary body, was demonstrated by our group. This paper reports experiments that characterize vitreous transferrin as one of these glycoproteins. Vitreous of rabbits injected intravitreally either with H-3-fucose or H-3-tyrosine and killed 40 hr after the injection was processed for ID and 2D-electrophoresis, followed by immunoblot techniques or fluorography. Tt was possible to detect a labeled polypeptide with the same molecular weight and pi of rabbit plasma transferrin. Furthermore, this labeled polypeptide could be specifically eluted from columns of Sepharose conjugated with antibody against rabbit plasma transferrin. Thus, these results demonstrate that at least part of the transferrin of the vitreous is synthesized within the eye.
