The plasma membrane H+‐ATPase from maize roots is phosphorylated in the C‐terminal domain by a calcium‐dependent protein kinase |
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| Authors: | Lorenzo Camoni Maria Rosaria Fullone Mauro Marra Patrizia Aducci |
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| Institution: | L. Camoni, M. Marra and P. Aducci (corresponding author, e‐mail;), Dipartimento di Biologia, Univ. di Roma "Tor Vergata", Via della Ricerca Scientifica, I‐00133, Roma, Italy;M. R. Fullone, Dipartimento di Scienze Biochimiche "A. Rossi Fanelli", Univ. di Roma "La Sapienza", P.le A. Moro 5, I‐00185 Roma, Italy. |
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| Abstract: | A protein kinase activity associated with maize root plasma membranes was partially purified and characterized. Biochemical properties, such as calcium dependence, inhibition by calmodulin antagonists, and absence of calmodulin stimulation, indicated that the enzyme belongs to the calcium‐dependent protein kinase (CDPK) family. By means of an in‐gel phosphorylation assay the molecular mass of active polypeptides was determined: two bands of 55 and 51 kDa became labelled. The same proteins were also immunodecorated by monoclonal antibodies against soybean CDPK. Results from in vitro assays demonstrated that maize H+‐ATPase was a suitable substrate for this protein kinase and that the phosphorylation site was located at the C‐terminal domain of the enzyme. This result was confirmed by using as substrate in phosphorylation assays the isolated C‐terminal domain of the H+‐ATPase expressed in Escherichia coli as a glutathione‐transferase fusion protein. |
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