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

• Published in: Free radical biology & medicine Vol. 8; no. 3; pp. 217 - 222
• Main Authors: Murakami, Koko, Jahngen, Jessica H., Lin, Sharon W., Davies, Kelvin J.A., Taylor, Allen
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 1990; Elsevier Science
• Subjects: Aging; Alpha-crystallin; Analytical, structural and metabolic biochemistry; Animals; Biological and medical sciences; Cattle; Crystallins - metabolism; Cysteine Endopeptidases - metabolism; Eye; Fundamental and applied biological sciences. Psychology; High molecular weight protease; Holoproteins; Hot Temperature; Hydrolysis; Hydroxides; Irradiation; Lens; Lens, Crystalline - metabolism; Macroxyproteinase (M.O.P.); Multienzyme Complexes - metabolism; Other proteins; Oxidation; Oxidative stress; Protease Inhibitors - pharmacology; Proteasome Endopeptidase Complex; Proteins; Proteolysis; Oxidative stress; SCMBSA; DTT; kDa; PCMB; MOP; Eye; SDS-PAGE; BSA; RBC; TCA; Proteolysis; PMSF; Macroxyproteinase (M.O.P.); NEM; Irradiation; Aging; Lens; Oxidation; High molecular weight protease; Alpha-crystallin; Bovine; Multienzyme complex; Proteins; Vertebrata; Regulation(control); Mammalia; Crystallin; Enzymatic digestion; Artiodactyla; Ungulata
• ISSN: 0891-5849; 1873-4596
• DOI: 10.1016/0891-5849(90)90066-R

Proteasome, a high molecular weight protease complex (HMP, ≈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°C, mostly to trichloroacetic acid precipitable polypeptides. The proteasome, thus isolated, was labile at 55°C. As indicated by the ability of p-chloromercuribenzoate and N-ethylmaleimide to block activity, a thiol group is required for activity. Alpha-crystallin was oxidized by exposure to 60Co-irradiation under an atmosphere of N 2O (1–50 kilorads). This dose delivered 0.1–5.7 mol of hydroxyl radicals per mol of crystallin. Irradiation resulted in increased heterogeneity, aggregation, and fragmentation of the crystallin preparation. The proteolytic susceptibility of alpha-crystallin to the lens HMP was enhanced by the irradiation in a dose-dependent manner up to 20 kilorads ( .OH concentration up to 2.3 mol per mol of alpha-crystallin). When 50 kilorads (5.7 mol .OH per mol of alpha-crystallin) was used, there was extensive aggregation and no enhancement in proteolysis over the unirradiated sample. The data indicate that the lens HMP can degrade mildly photooxidized lens proteins, but proteins which are extensively damaged are not degraded and may accumulate. This may be related to cataract formation.