Étude comparée de la dénaturation de la pepsine en solution et en surface I. Influence du pH sur la dénaturation en solution

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Abstract
Physicochemical data of diluted pepsin solutions have been estimated in function of the pH.Below pH 5, 5 (native pepsin), and in the range pH 7‐10 (denatured pepsin) the solutions appear homogeneous in the ultracentrifuge. In the range pH 6,25‐7, the solutions are heterogeneous, and, this is due to hydrolysis of denatured pepsin by still active native pepsin.Hydrodynamical properties, S, D and [η] have been calculated for the native and completely denatured pepsin. Molecular weights estimated by the Svedberg equation agree at pH 5, 2, and at pH 7,2‐8,3 (27.000). Light scattering studies give a molecular weight of 35.000 at pH 2,55 and in KCl 0,15 M. In a four components system at pH higher than 5 the values of C/τ are too small indicating aggregation or strong electro‐static interactions.The observed increase of [η] and decrease of S and D for denatured samples t to a swelling of the molecule. Moreover for native pepsin it is confirmed that it is difficult to estimate the axial ratio and the hydration.Finally, aggregation of denatured pepsin by lowering the pH is discussed on the basis of sedimentation and turbidity measurements.