The redox-controlled light-harvesting chlorophyll a/b protein kinase. Deactivation by substituted quinones.
The deactivation of the redox-controlled light-harvesting chlorophyll a/b protein kinase of Acetabularia acetabulum and pea thylakoids was studied. Substituted benzoquinone, naphthoquinone, and anthraquinone analogs including mono-, di-, and trihalogenated and/or alkylated quinones, which are known to inhibit the cytochrome b6/f activity, deactivate the kinase in the dark, and prevent its activation in the light. Analogs halogenated at positions 2- or 3- are the most effective deactivators. Increasing the size of the alkyl side chain and/or the number of rings lowers the deactivation effect. The activated state of the pea kinase decays with a t1/2 of 15 min, while the Acetabularia enzyme retains its active state for at least 2 h. The midpoint potential for Acetabularia kinase activity in the dark is 120 +/- 10 mV and is compatible with the involvement of plastoquinone in the kinase activation via reduction of the cytochrome complex. Deactivation of kinase by the analogs inhibiting cytochrome b6/f complex activity and the kinase copurification with the cytochrome b6/f fraction obtained from the Acetabularia thylakoid further support this conclusion. These results indicate that the process of kinase activation/deactivation includes the binding of plastoquinol or quinone analogs by the cytochrome complex and its interaction with the kinase. We propose that the latter process may constitute the rate-limiting step controlling the kinase activation/deactivation kinetics.
Frid
D
D
Department of Biological Chemistry, Hebrew University, Jerusalem, Israel.
Gal
A
A
Oettmeier
W
W
Hauska
G
G
Berger
S
S
Ohad
I
I
D000076:Acetabularia / Q000201:enzymology*; D003573:Cytochrome b Group / Q000302:isolation & purification / Q000378:metabolism; D045346:Cytochrome b6f Complex; D004789:Enzyme Activation; D004795:Enzyme Stability; D007700:Kinetics; D046911:Macromolecular Substances; D010084:Oxidation-Reduction; D010766:Phosphorylation; D011199:Potentiometry; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases / Q000302:isolation & purification / Q000378:metabolism*; D011809:Quinones / Q000494:pharmacology*; D013329:Structure-Activity Relationship; D013997:Time Factors
D003573:Cytochrome b Group; D046911:Macromolecular Substances; D047428:Protein Kinase Inhibitors; D011809:Quinones; D045346:Cytochrome b6f Complex; D011494:Protein Kinases