Effect of aspect ratio on protein diffusion in hydrogels

To elucidate the effect of the aspect ratio of protein on the diffusion in gels, the diffusion of a rodlike protein, tropomyosin, in two kinds of poly saccharide gels, agarose and carrageenan, has been investigated by electron ic speckle pattern interferometry method and compared with that of a globul ar protein, myoglobin. In an agarose gel that has a comparatively large por e size, the diffusion coefficient D of the tropomyosin (aspect ratio R = 26 ) shows a behavior similar to that of the globular myoglobin (R = 1.6), dec reasing with the fiber volume fraction phi with a scaling exponent alpha = -0.3 to -0.4, which is close to the Rouse model of alpha = -0.5. Whereas in the lambda -carrageenan gel that has a smaller pore size, the diffusion of tropomyosin is quite different from that of myoglobin and consists of two regions: a region at a low fiber volume fraction D approximate to phi (-0.3 ), close to the Rouse model and a region at a high fiber volume fraction D approximate to phi (-1.8), close to the reptation model of alpha = -1.75. A s far as the authors know, this is the first reptationlike behavior observe d for the diffusion of rodlike protein in a hydrogel.