Proton Magnetic Resonance Spectra of Porcine and Bovine Insulin and of the A and B Chain of Bovine Insulin

This paper shows that reproducible proton magnetic resonance spectra of a low molecular protein, insulin, and of medium sized polypeptides (insulin A and B chains) can be recorded and interpreted consistently in terms of proton resonances from chemically different hydrogen atoms. For example, porcine and bovine insulin proton magnetic resonance spectra differ. The experimental procedure adopted has been to accumulate 100 to 400 single spectra from a standard Varian A-60 spectrometer on a computer, C-1024, thus improving the otherwise prohibitive signal to noise ratio. The denaturing agent, CF 3 COOH, was used as solvent in order to minimize the line broadening from which spectra of aqueous solutions suffer. This strong acid reacts with insulin as shown by fluorine resonance experiments, but slowly enough to permit conclusive experiments within 3 to 4 hours at 27°. The occurrence of spin-split signals from methyl and phenyl group protons and an estimate of the total signal response from the insulin protons indicate high intramolecular mobility for insulin dissolved in CF 3 COOH.