In classic experiments that helped convince investigators that the proton, artif

Question

In classic experiments that helped convince investigators that the proton, artificial membrane vesicles were reconstituted with purified bacteriorhodopsin (which is a light- driven H+ pump from a photosynthetic bacterium) and purified ATP synthase from ox heart mitochondria. In these vesicles the membrane complexes are oriented so that protons are pumped into the vesicle and ATP synthesis occurs on the outer surface. When ADP and Pi were added to the medium surrounding the vesicles and the vesicles were illuminated with appropriate light, the interior of the vesicles became acidic and ATP was produced.

A. Explain what is happening when the vesicles are illuminated. Why does the interior of the vesicle become acidic? How is ATP being produced?

B. If, instead, the ATP synthase molecules were randomly oriented so that about half faced the outside of the vesicle and half faced the inside, would you expect ATP to be synthesized? Explain your answer.

C. If the bacteriorhodopsin molecules were randomly oriented, would you expect ATP to be synthesized? Explain your answer.

Explanation / Answer

B.) If ATP syhthetase molecules were randaomly oriented so that about half faced the outside of the vesicle and half faced the inside ATP is synthesised about half the rate. The ATP synthetasein correct orientation would make up ATP where as orientation in opposite direction make the enzyme inert.

C.) If bacteriorhodopsin molecules were randomly oriented very less ATP is synthesised. In vesicles with equal numbers of oppositely oriented Bacteriorhodopsin molecules pH difference is not generated upon exposure to light because proton pumping in both directions is equal. The excess pumping of protons in outward direction , pH difference is in wrong direction to be utilised by ATP synthase and ATP is not synthesised.

With excess inward movement of protons PH difference is in right direction thus ATP synthase utilise protons and thus ATP is synthesised.

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