Studies on the polarography of proteins. 1. The relation of wave heights to protein concentration and the origin of wave III

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Abstract
Polarograms were recorded in 0.001 [image] CoCl2 and ammonia buffer at pH 9.6 for the following proteins: insulin, pepsin, bovine plasma albumin, chymotrypsin and trypsin. The heights of all waves are reported. The Langmuir adsorption isotherm equations were calculated for the curves relating the wave height to the protein concn. for the 3 waves I, II and III. The relation between the Langmuir constant B and the vol. of the protein aggregate suggests that the protein interferes with the diffusion of Co-ammonia complexes when the protein concn. is high and that the magnitudes of waves I and II are limited by the size of the protein aggregate. BII is linearly related to the ratio (total potential sulfydryl groups/vol. of protein aggregate) which implies that all the potential sulfydryl groups of the protein are available polaro-graphically. Acetylation of insulin amino groups by ketene depresses the apparent adsorption of the protein on the electrode surface. The depression of BIII by acetylation of the protein or by the addition of formaldehyde to the electrolyte and the appearance of "prenatrium" waves in the polarograms of certain organic compounds suggest that wave III depends upon the presence of nitrogenous groups rather than sulfydryl groups.