Investigations of sources of error in the estimation of tyrosine and tryptophan in complex materials, which are associated with hydrolysis

Abstract

In tests of recovery of tyrosine and tryptophane from digestion at 100[degree] in (a) 7N H2SO4, (b) 5N NaOH and (c) NaOH-stan-nite reagent, for 20-50 hr., there was no decomposition of tyrosine, but some decomp. of tryptophane in (a), less in (b) and least in (c). Additions of other amino-acids were without effect; carbohydrate was without effect in (b) and (c), but in (a) caused considerable loss of tyrosine and almost complete loss of tryptophane. Tests with edestin (and with other protein preps., details of which are not given) indicate that tryosine and tryptophane are liberated from peptide linkages by (b) and (c) within 30 hr. Addition of carbohydrate is without effect. Tyrosine is liberated also from glycoside linkage (O-[beta]-glucosidotyrosine was used in test). Diiodotyrosine does not yield tyrosine in (b) if reducing substances are excluded, but is quantitatively reduced to tyrosine in (c). Recommended hydrolysis procedures for the subsequent estimation of tyrosine (and diiodotyrosine) and tryptophane, with provision for the extraction of extraneous phenols and indoles, are given. Errors are discussed and corrections indicated.