| Abstract: | Small-angle neutron scattering experiments were performed in dilute aqueous solutions of chloroplast F1-ATPase. By contrast variation in 1H2O/2H2O mixtures and when using different concentrations of glycerol in 2H2O, structural information on the spatial distribution of dry protein and water was obtained. The maximum distance within latent and active CF1 was 12 nm. the shape of CF1 was globular. The total volume of CF1 was 900 nm3, and its dry volume (excluding the volume of one water molecule per two exchangeable hydrogen atoms) was 400 nm3. A volume of 670 nm3 was inaccessible to glycerol at low glycerol concentrations (less than 25%). At higher concentrations (up to 50%) a volume of 460 nm3 was excluded to glycerol. Within the resolution of our experiment (1.6 nm) there was no evidence for particular water-rich regions or of secluded water spaces or any particular places for glycerol exchange. Upon thiol activation of the latent enzyme only small changes in structure were detectable just at the limits of the experimental error. They suggest an enhancement of the surface roughness. |
