Lens proteasome shows enhanced rates of degradation of hydroxyl radical modified alpha-crystallin.

Proteasome, a high molecular weight protease complex (HMP, approximately 600 kDa) was isolated from bovine eye lens epithelium tissue. In contrast with prior reports, lens proteasome degraded the major lens protein alpha-crystallin and S-carboxymethylated bovine serum albumin at 37 degrees C, mostly to trichloroacetic acid precipitable polypeptides. The proteasome, thus isolated, was labile at 55 degrees C.

Aging and cellular maturation cause changes in ubiquitin-eye lens protein conjugates.

The eye lens is a useful tissue for studying phenomena related to aging since it can be separated into differentially aged or matured zones. This work establishes correlations between ubiquitin-lens protein conjugating capabilities and age, as well as the stage of maturation of bovine lens tissue. When exogenous 125I-ubiquitin was combined with supernatants of epithelial (least mature), cortex, and core (most mature) tissue, ATP-dependent conjugation of 125I-ubiquitin to lens proteins was most effective with the epithelial tissue preparation.

Properties of the ubiquitin conjugation system from bovine eye lens.

A post-translational protein modification system involving the polypeptide ubiquitin results in ubiquitin-protein conjugates of various functions. A ubiquitin-conjugating enzyme system was isolated from the epithelial tissue of bovine eye lens by DEAE-Sepharose and Bio-Gel A-1.5m column chromatography.

The eye lens has an active ubiquitin-protein conjugation system.

Using exogenous 125I-ubiquitin, ubiquitin-lens protein conjugation was observed with supernatants of cultured rabbit lens epithelial cells and lens cortex tissue. Conjugation was ATP-dependent with the greatest variety and amount of conjugates larger than 150 kDa. In vivo production of ubiquitin-protein conjugates in cultured rabbit and beef lens epithelial cells and rabbit lens tissues of different developmental age was established using immunological detection.

Lens proteins are substrates for the reticulocyte ubiquitin conjugation system.

In the aged lens postsynthetically altered molecules comprise the majority of lens proteins. Many proteolytic activities have been observed in lens supernatants. Since damaged or altered proteins are usually selectively and rapidly degraded in other cells and tissues, the accumulation of these species in the lens seemed enigmatic.