The multiple alternative oxidase proteins of soybean

The identity of the multiple alternative oxidase bands detected in various soybean tissues was investigated to determine if any modification that can alter the mobility on SDS-PAGE of the alternative oxidase occurs after mito chondrial import other than removal of the presequence. Comparison of the m ature, in vitro imported products of AOX1, AOX2 and AOX3 in soybean cotyled ons and rat liver mitochondria indicated that they had an identical apparen t molecular mass to their in vitro expressed mature forms. This suggests th at no modification specific to plant alternative oxidase altering the mobil ity on SDS-PAGE, took place. Changing the -2 and/or -3 Arg residue resulted in the inhibition of the generation of this mature form, suggesting that p rocessing was most likely by the general mitochondrial processing peptidase . Comparison of the in vitro expressed mature forms to that detected by imm unoblots of soybean tissues, required the induction of AOX1. Treatment of s oybean cultured cells with antimycin A resulted in the induction of an addi tional band cross-reacting to monoclonal antibodies against the alternative oxidase. Comparison of the in vitro expressed mature forms to the alternat ive oxidase detected by western blotting indicated that they were identical in apparent molecular mass. These results indicated that no modification o ther than presequence removal, which alters mobility on SDS-PAGE, was requi red to generate the mature functional alternative oxidase proteins.