ALPHA-A-CRYSTALLIN AND ALPHA-B-CRYSTALLIN IN THE RETINA - ASSOCIATIONWITH THE POST-GOLGI COMPARTMENT OF FROG RETINAL PHOTORECEPTORS

alpha A- and alpha B-Crystallins are significant contributors to maint aining the transparency of the vertebrate lens. We have found that bot h alpha A- and alpha B-crystallins are also present, at approximately equimolar concentrations, in frog retinal cells. They were identified by sequencing portions of each polypeptide, by immunochemical cross-re activity with antibodies to bovine alpha-crystallins, and by their rel ative mobility in two-dimensional gel electrophoresis. Retinal alpha-c rystallins form macromolecular multimeric complexes similar to those f ound in the lens, and they are abundant both in soluble and membrane-a ssociated forms. A surprising finding is that alpha-crystallins bind s pecifically to the photoreceptor post-Golgi membranes that mediate tra nsport of newly synthesized rhodopsin. Upon treatment of post-Golgi me mbranes with urea or Triton X-114, a portion of the bound alpha B-crys tallin remains tightly associated, indicating that the alpha B-form ma y mediate membrane binding of an alpha-crystallin multimeric complex. Both subunits are synthesized in vitro by isolated frog retinas, but a lpha B-crystallin appears to have a higher renewal rate. Newly synthes ized alpha-crystallins become associated with the post-Golgi membranes concurrently with newly synthesized rhodopsin. Association of alpha-c rystallins with newly synthesized rhodopsin suggests that they may par ticipate in photoreceptor outer segment membrane renewal. Our findings implicate an important function for both alpha A- and alpha B-crystal lins in the same, extralenticular, tissue.