The Labile Sulfur of Insulin.

Abstract

All observers agree that insulin material contains sulfur and Abel1 has shown that sulfur is present in a very labile form, being split off as a sulfide by boiling with weak alkali. Abel believes that the sulfur is roughly proportional to the hypoglycemic potency. Brand and Sandberg2 have shown that although the sulfur of cystine is relatively stable, the linkage of other amino acids with cystine so affects the sulfur that it is easily split out by boiling with weak alkali. Cystine can be determined quantitatively by the uric acid reagent of Folin and Denis, as shown by Folin and Looney.3 The cystine is first reduced by sodium sulfite in saturated sodium carbonate to cysteine which then gives a deep blue color with the phosphotungstic acid reagent. Shonle and Waldo4 found that insulin preparations respond to this test for cystine.I have observed that insulin preparations do not give the reaction directly with the uric acid reagent but do so after reduction with sulfite. The insulin material upon boiling f...