TY - JOUR
T1 - The interaction between bicarbonate and the herbicide ioxynil in the thylakoid membrane and the effects of amino acid modification on bicarbonate action
AU - Vermaas, Wim F.J.
AU - Van Rensen, Jack J.S.
AU - Govindjee,
N1 - Funding Information:
The \[14C\]ioxynil-b.inding studies were performed in the laboratory of Dr. Charles J. Arntzen (MSU-DOE Plant Research Laboratory, East Lansing, MI 48824, U.S.A.). We are thankful to him for his hospitality and for fruitful discussions. \[lnc\]Ioxynil was a generous gift from May & Baker, U.K. This research was supported by an NSF grant (78-24532) to G.
PY - 1982/8/20
Y1 - 1982/8/20
N2 - Bicarbonate depletion of chloroplast thylakoids reduces the affinity of the herbicide, ioxynil, to its binding site in Photosystem (PS) II. This herbicide is found to be a relatively more efficient inhibitor of the Hill reaction when HCO-3 is added to CO2-depleted thylakoids in subsaturating rather than in saturating concentrations. The reason for this dependence of the inhibitor efficiency on the HCO-3 concentration is that the inactive HCO-3-deficient PS II reaction chains bind less ioxynil than the active PS II electron-transport chains that have bound HCO-3, and, thus, after addition of a certain amount of ioxynil the concentration of the free herbicide increases when the HCO-3 concentration decreases. Therefore, the inhibition of electron transport by ioxynil increases at decreasing HCO-3 levels. Measurements on the effects of modification of lysine and arginine residues on the rate of electron transport are also presented: the rate of modification is faster in the presence than in the absence of HCO-3. Therefore, we suggest that surface-exposed lysine or arginine residues are not involved in binding of HCO-3 (or CO2 or CO2-3) to its binding protein, but that HCO-3 influences the conformation of its binding environment such that the affinity for certain herbicides and the accessibility for amino acid modifiers are changed.
AB - Bicarbonate depletion of chloroplast thylakoids reduces the affinity of the herbicide, ioxynil, to its binding site in Photosystem (PS) II. This herbicide is found to be a relatively more efficient inhibitor of the Hill reaction when HCO-3 is added to CO2-depleted thylakoids in subsaturating rather than in saturating concentrations. The reason for this dependence of the inhibitor efficiency on the HCO-3 concentration is that the inactive HCO-3-deficient PS II reaction chains bind less ioxynil than the active PS II electron-transport chains that have bound HCO-3, and, thus, after addition of a certain amount of ioxynil the concentration of the free herbicide increases when the HCO-3 concentration decreases. Therefore, the inhibition of electron transport by ioxynil increases at decreasing HCO-3 levels. Measurements on the effects of modification of lysine and arginine residues on the rate of electron transport are also presented: the rate of modification is faster in the presence than in the absence of HCO-3. Therefore, we suggest that surface-exposed lysine or arginine residues are not involved in binding of HCO-3 (or CO2 or CO2-3) to its binding protein, but that HCO-3 influences the conformation of its binding environment such that the affinity for certain herbicides and the accessibility for amino acid modifiers are changed.
KW - (Pea chloroplast)
KW - Bicarbonate effect
KW - Herbicide
KW - Photosystem II
KW - Protein modification
KW - Thylakoid membrane
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U2 - 10.1016/0005-2728(82)90028-7
DO - 10.1016/0005-2728(82)90028-7
M3 - Article
AN - SCOPUS:0020399310
VL - 681
SP - 242
EP - 247
JO - Biochimica et Biophysica Acta - Bioenergetics
JF - Biochimica et Biophysica Acta - Bioenergetics
SN - 0005-2728
IS - 2
ER -