Molecular Weight of Insulin in N,N-Dimethylformamide

Abstract

THE detailed investigations of Sanger and co-workers have established the molecular weight of insulin as some multiple of about 6,000 ¹. It is not clear, however, whether the fundamental covalently bonded unit is the 6,000 or 12,000 species. (The determination of the positions of the S—S linkages in insulin¹ does not establish the fundamental unit as the 6,000 species. The methods of analysis do not preclude the possibility of a staggered arrangement of the S—S linkages such that the 12,000 species is covalently bonded together.) Several workers using a variety of techniques—osmotic pressure, sedimentation and light-scattering—achieved results indicating that the minimum molecular weight of insulin in aqueous solution is 12,000 ². However, other work has indicated a value of 6,000. Harfeneist and Craig³, by counter-current distribution methods in 2-butanol-dichloracetic acid systems, Fredericq⁴ by sedimentation-diffusion studies in alkaline solutions, and Kupke and Linderstrøm-Lang⁵ by osmotic pressure determinations in aqueous guanidine chloride solutions, have all recently contributed data consistent with the value of 6,000. Osmotic pressure studies of insulin in N,N-dimethylformamide in this laboratory also indicate a molecular weight of 6,000 for the fundamental unit.