Summary: The gas permeability coefficient of the cyanobacterial gas vesicle wall has been determined by comparing the concentration gradient of oxygen gas in a film of gas vesicles with the gradient in an underlying film of agar supported over an oxygen atmosphere. The gradients were determined with an oxygen microelectrode. The value of the gradient in aqueous agar was 0·81 of that in a suspension in which gas vesicles occupied 0·35 of the total volume. From this it was calculated that the notional diffusivity of oxygen through the gas vesicle was equivalent to 0·53 of the diffusivity in water. The permeability coefficient of the gas vesicle membrane is calculated to be = 32 mm , the rate coefficient for filling the gas vesicle by diffusion is a = 2·4 x 10 and the folding time for equilibration of gas into a gas vesicle is = 0·4 μs. The permeability coefficient is about 100-fold higher than the minimum value set by previous pressure rise experiments, and confirms that gas vesicles could not store gas. The measurements also show, however, that randomly oriented gas vesicles would not provide a diffusion channel with a diffusivity higher than that in water, although a layer of gas vesicles oriented with their long axes parallel to the diffusion gradient would provide a diffusivity 3·5-fold higher. The determination of the diffusivity was made with a theory, based on diffusion equations, which can be used in the determination of the diffusivity through other cell organelles.


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