Multicatalytic proteinase complex (MPC; Proteasome) in bovine and chick lens: B.J. Wagner, J.W. Margolis and I. Singh Depts. of Biochem. & Mol. Biol. and Ophthalmol., UMDNJ-New Jersey Med. School, Newark, NJ USA

Abstract

Lenses from Rhesus monkeys were maintained in protein-free medium and both their biochemical and histological changes were examined. Lenses were dissected under a dissecting microscope to ensure minimal contamination by other ocular tissue, which allowed successful observation of whole lens morphology during culture. Lenses in culture showed no acute leakage of protein into medium, indicating that they had not been physically damaged during dissection. Cultured lenses remained transparent for 21 days without any noticeable histological changes. Even at 21 days of culture,35S-methionine incorporation into lens protein was approximately 60% of the level observed in fresh lenses. The amounts of most protein species were rather constant in the lens capsule/epithelium throughout culture, but the amount of crystallins gradually decreased during the first 14 days of culture due to selective decrease in crystallin synthesis. After day 14, both the amount of crystallins and their synthesis became stable. When 30 mM fructose, present in the control medium, was replaced with 30 mM xylose, lens opacification with some histological abnormalities such as vacuole formation was observed. In the xylose-induced cataract, the protein synthetic activity decreased dramatically. This system would be a valuable tool in investigating the mechanisms of lens homeostasis as well as mechanisms of cataractogenesis in primate lens.