The reversible dissociation of insulin and its minimum molecular weigh

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Abstract
It has been shown that the degree of aggregation of insulin in solns. depends not only upon pH, temp. and insulin concn. but also upon the electrolyte concn. and the type of electrolyte present in the soln. At the optimum pH for dissociation (pH 2.5-2.7) the molecular wt. calculated from osmotic pressure measurements extrapolated to zero protein concn. is about 12,000, irrespective of salt concn. The molecular wt. at finite protein concn. is, however, larger the greater the salt concn. There is some indication that NaCl has a more marked effect on the aggregation than phosphates. The sedimentation constant of insulin under conditions of max. dissociation was found to be 1.65 x 10-13, which is likely to be the sedimentation constant for the homogeneous unit for M = 12,000. Some general features of reversible changes occurring in solns. of crystalline proteins are discussed together with structural information which can be adduced from them.
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