Phosphoproteins and Protein Kinase Activities Intrinsic to Inner Membranes of Potato Tuber Mitochondria

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Inside-out submitochondrial particles (IO-SMP) were isolated and purified from potato (Solanum tuberosum L.cv.) tubers. When these IO-SMP were incubated with [γ-^<32>P]ATP more then 20 proteins became labelled as a result of phosphorylation. The ^<32>P incorporation was stimulated by the oxidising reagent ferricyanide. Except for a 17 kDa protein which was phosphorylated only in the absence of divalent cations, the protein phosphorylation required Mg^<2+>. The time for half-maximum ^<32>P incorporation was 4 min for the 22 kDa phospho-F_1 δ-subunit and 2 min for the 28 kDa phospho-F_0 b-subunit of the proton-ATPase. The K_m for ATP for the detected phosphoproteins was between 65 μM and 110 μM. The pH optimum for protein phosphorylation in inner membranes was between pH 6 and 8, and for the F_1 δ-subunit and the F_0 b-subunit the pH optima were 6.5-8 and pH 8, respectively. A 37 kDa phosphoprotein was phosphorylated on a histidine residue while the remainder of the inner membrane proteins were phosphorylated on serine or threonine residues. Two autophosphorylated putative kinases were identified: one at 16.5 kDa required divalent cations for autophosphorylation, while another at 30 kDa did not. A 110 kDa protein was labelled only with [α-^<32>P]ATP, suggesting adenylylation.
日本植物生理学会の論文