The terminal peptides of insulin

Abstract

While this work was in progress an outline of a fluorimetric method for the determination of N- methyl-2-pyridone-5-carboxylamide in urine was reported by Rosen, Perlzweig & Handler (1948).The authors considered that their values for normal urines (5.0-13.2mg./day) may have been somewhat low, but it is obvious that they are of the same order as those obtained by the present colorimetric method (see Table 1, and also Dean & Holman, 1949).SUMMARY 1. Methods are described for the determination of N-methyl-2-pyridone-5-carboxylamide and N- methyl-2-pyridone-3-carboxylamideinhuman urine.The methods are based on the nitration of the com- pounds, after isolation from urine by adsorption on Lloyd's reagent followed by extraction with chloro- form, and on their colorimetric determination by means of the yellow colours given by the nitro derivatives in alkaline solution.2. The accuracy and specificity of the methods is discussed.3. Results are shown which indicate that the 2:3- amide is of no significance in nicotinic acid meta- bolism, but that the 2:5-amide is an important meta- bolite.The 2:5-amide was excreted by two normal adults in amounts of the order of 7 mg./24hr.After the ingestion of 500 mg.ofnicotinamide, the urinary excretion of the 2:5-amide increased greatly, 47- 57 % of the dose being excreted in 72 hr. as the latter compound.4. It was possible to account for 73-80 % of an orally administered dose of 500 mg. of nicotinamide in the urine of two adult subjects as N-methyl-2- pyridone-5-carboxylamide, N-methylnicotinamide and the total acid-hydrolysable derivatives of nicotinic acid.