?The activity of the Chloroplastic Ndh Complex is Regulated by Phosphorylation of the NDH-F subunit?

LASCANO, H.R.. ; LEONARDO M. CASANO, ; MERCEDES MARTIN; BARTOLOME SABATER

PLANT PHYSIOLOGY.

American Society of Plant Biologists

Año: 2003 p. 256 - 262

0032-0889

Hydrogen peroxide (H2O2) induces increases, to different degrees, in transcripts, protein levels, and activity of the Ndhcomplex (EC 1.6.5.3). In the present work, we have compared the effects of relatively excess light, H2O2, dimethylthiourea(a scavenger of H2O2), and/or EGTA (a Ca2 chelator) on the activity and protein levels of the Ndh complex of barley(Hordeum vulgare cv Hassan) leaf segments. The results show the involvement of H2O2 in the modulation of both the proteinlevel and activity of the Ndh complex and the participation of Ca2 mainly in the activity regulation of pre-existing protein.Changes in Ndh complex activity could not be explained only by changes in Ndh protein levels, suggesting posttranslationalmodifications. Hence, we investigate the possible phosphorylation of the Ndh complex both in thylakoids and in theimmunopurified Ndh complex using monoclonal phosphoamino acid antibodies. We demonstrate that the Ndh complex isphosphorylated in vivo at threonine residue(s) of the NDH-F polypeptide and that the level of phosphorylation is closelycorrelated with the Ndh complex activity. The emerging picture is that full activity of the Ndh complex is reached byphosphorylation of its NDH-F subunit in a H2O2- and Ca2-mediated action.