Preparation and properties of alpha- and epsilon-amino-protected porcine relaxin derivatives.

The chemical modification of the amino groups of B29 porcine relaxin resulted in pure derivatives of N alpha A1-citraconyl-B29 relaxin, N epsilon A7, N epsilon A16, N epsilon B8-tris [[[(methylsulfonyl)ethyl]oxy]carbonyl]-B29 relaxin (Msc3-relaxin), and N alpha A1, N epsilon A7, N epsilon A16, N epsilon B8-tetrakis [[[(methylsulfonyl)ethyl]oxy]carbonyl]-B29 relaxin (Msc4-relaxin). N alpha A1-Citraconyl-B29 relaxin was obtained after selective deprotection of fully acylated B29 relaxin derivatives. The quantitative reaction of N alpha A1-citraconylrelaxin with [[(methylsulfonyl)ethyl]-oxy]carbonyl succinimide ester followed by deprotection of the citraconyl group resulted in N epsilon A7, N epsilon A16, N epsilon B8-Msc3-B29 relaxin, the starting material for selective chemical modifications at the N terminus of the relaxin A chain. In mouse interpubic ligament assay both Msc3 and Msc4 derivatives of relaxin showed a bioactivity of 30%, while in the case of N alpha A1-citraconyl-B29 relaxin the bioactivity was reduced to 15%. When compared with unmodified relaxin, only the circular dichroic spectrum of N alpha A1-citraconyl-B29 relaxin revealed significant differences. Therefore, the loss in bioactivity of the N alpha A1-citraconyl-B29 relaxin seems to be related to the structural changes caused by the introduction of a negative charge at the N terminus of the A chain.