REGULATION OF PHOSPHORYLATION OF WHEAT MITOCHONDRIAL PROTEINS BY DIVALENT-CATIONS

Mitochondria isolated from 4-day-old dark-grown wheat seedlings were p urified by self-generating Percoll gradient. Phosphorylation reaction was carried out in vitro with the addition of [ c-P-32]ATP and polypep tides 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 dephosphor ylation of 120 and 66 kD polypeptides but, simultaneously, induced/enh anced the phosphorylation of some polypeptides, with the effect being more pronounced on a 67 kD species. The phosphorylation of 120 kD spec ies and a few other polypeptides was also down-regulated and that of a 18 kD polypeptide was up-regulated by Ca2+. The present study provide s evidence that phosphorylation status of mitochondrial proteins is re gulated by Mg2+ and/or Ca2+-dependent phosphatase(s) and protein kinas e(s).