Abstract
Utilizing the reaction of its secondary amino group, proline in proteins was determined in the presence of other amino acids. The material proteins were first hydrolyzed and then allowed to react with nitrous acid to convert the proline therein into N-nitrosoproline, when all the other amino acids were changed into the corresponding hydroxy acids. N-Nitrosoproline was then reduced to N-aminoproline with zinc dust and hydrochloric acid, and finally the N-amino compound was determined by azotometry by oxidation with potassium ferricyanide. Incidentally, the secondary amino group in the ring of tryptophan, histidine, and prolidine, and the guanidine group of arginine do not interfere with the present method.
