Synthesis of peptides containing cystine and glutamine, with remarks on their possible bearing on the structure of insulin and a note on the amide nitrogen of insulin

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Abstract
Cystylglutamine and glutaminyleystine were synthesized and the labilities of their S and amide N were compared with those of insulin. The S of insulin is much less stable towards alkali than that of either of the peptides; the proportions of N liberated as NH3 by treatment with alkali are similar for insulin and glutaminylcystine but lower for cystylglutamine. Neither of the synthetic peptides has any hypoglycemic action. Little support is therefore afforded by these expts. for the view that a grouping similar to one or other of these peptides exists in insulin. Detn. of the amide N of insulin gives a value of about 34 groups per molecule (of mol. wt. 35,100) ; assuming the absence of aspartic acid their value, in combination with recent titration results, leads to the concl. that insulin contains about 30% of glutamic acid.

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