Differential inhibition of Pi-ATP exchange in relation to ATP synthesis and hydrolysis by modification of chloroplast thylakoid membranes with glutaraldehyde |
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Authors: | Dudy Bar-Zvi Noun Shavit |
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Institution: | Department of Biology, Ben-Gurion University of the Negev, Beer Sheva 84 105 Israel |
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Abstract: | Limited modification of thylakoid membranes with glutaraldehyde inhibits the Pi-ATP exchange reaction much more than ATP synthesis or hydrolysis. More extensive modification of the membranes results in the inhibition of all activities of the ATP synthetase, but does not affect electron transport. Limited modification also does not have much effect on the tight binding of 3H]ADP or the ΔpH supported by ATP hydrolysis. The modification affects the catalytic process itself and not the activation of the latent enzyme. Cross-linking between thylakoid polypeptides is observed only after extensive treatment with glutaraldehyde, while limited modification does not result in cross-linking between polypeptides. The differential inhibition of the Pi-ATP exchange relative to ATP hydrolysis can be explained by the decrease in only one of the kinetic rate constants involved in these reactions. However, the relative insensitivity of photophosphorylation to the modification suggests that different enzyme conformations may participate in phosphorylation (light) and ATP hydrolysis or Pi-ATP exchange (dark). |
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Keywords: | Glutaraldehyde Thylakoid modification ATPase Photophosphorylation Chemical modification Tricine Chl chlorophyll FCCP chloroplast coupling factor one (the hydrophilic portion of the ATP synthetase) |
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