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

The 26S proteasome was purified from cultured rice cells to near homogeneity by ultracentrifugation fo r5ha t85,000g, chromatography on Biogel A-1.5m, and glycerol density-gradient centrifugation analysis. The purified enzyme had two distinct forms, termed 26Sa- and 26Sb-type proteasomes, with different electrophoretic mobilities by nondenaturing polyacrylamide gel electrophoresis. It consisted of multiple polypeptides with molecular masses of 25‐35 and 42‐120 kDa, which presumably corresponded to those of the 20S proteasome and an associated PA700 regulatory complex, respectively. The rice 26S proteasome resembled, but was not identical to, one from other sources in their subunit composition and immunochemical reactivity. Intriguingly, both rice and spinach 26S proteasomes could not degrade rat ornithine decarboxylase in the presence of antizyme and ATP, unlike the rat 26S proteasome, implying the existence of functional differences between mammalian and plant 26S proteasomes. © 1999 Published by Elsevier Science Ireland Ltd. All rights reserved.