Metabolism of Rat Lens Crystallins

In order to ascertain the in vivo fate of lens proteins, 13-day-old rats were injected i.p. with 3 μCi of 1-14C-DL-valine, and the levels of radio-activity were monitored in the α-, β-, and γ-crystallins for approximately 10 months. The pattern of incorporation and subsequent disappearance of 14C-activity was similar for all 3 crystallins. The maximum detected rate of disappearance of each of the radiolabeled crystallins was approximately 5% per day. The rapid decrease in the rates of disappearance of the crystallins with aging suggests that the in vivo proteolytic activity of the lens is localized in the peripheral region and that the proteolytic activity of the lenscell is lost with age.