Regulation of Phosphorylation of Wheat Mitochondrial Proteins by Divalent Cations

Mitochondria isolated from 4-day-old dark-grown wheat seedlings were purified by self-generating Percoll gradient. Phosphorylation reaction was carried out in vitro with the addition of [c₋³²P]ATP and polypeptides resolved by SDS-PAGE were subjected to autoradiography. Amongst endogenous polypeptides phosphorylated, four polypeptides of 120, 66, 43 and 21 kD were prominent. Addition of Mg²⁺ (5 mM) caused dephosphorylation of 120 and 66 kD polypeptides but, simultaneously, induced/enhanced the phosphorylation of some polypeptides, with the effect being more pronounced on a 67 kD species. The phosphorylation of 120 kD species and a few other polypeptides was also down-regulated and that of a 18 kD polypeptide was up-regulated by Ca²⁺. The present study provides evidence that phosphorylation status of mitochondrial proteins is regulated by Mg²⁺ and/or Ca²⁺-dependent phosphatase(s) and protein kinase(s).