Purification and characterization of the 26S proteasome from cultured rice(Oryza sativa) cells

The 26S proteasome was purified from cultured rice cells to near homogeneit y by ultracentrifugation for 5 h at 85,000 x g, chromatography on Biogel A- 1.5m, and glycerol density-gradient centrifugation analysis. The purified e nzyme had two distinct forms, termed 36S alpha- and 26S beta-type proteasom es, with different electrophoretic mobilities by nondenaturing polyacrylami de gel electrophoresis. It consisted of multiple polypeptides with molecula r masses of 25-35 and 42-120 kDa, which presumably corresponded to those of the 20S proteasome and an associated PA700 regulatory complex, respectivel y. The rice 26S proteasome resembled, but was not identical to, one from ot her sources in their subunit composition and immunochemical reactivity. Int riguingly, both rice and spinach 26S proteasomes could not degrade rat orni thine decarboxylase in the presence of antizyme and ATP, unlike the rat 26S proteasome, implying the existence of functional differences between mamma lian and plant 26S proteasomes. (C) 1999 Published by Elsevier Science Irel and Ltd. All rights reserved.