Attempts to Isolate Dihydroxy-pyrrol-Alanine from Gelatin Hydrolysates

Abstract

Van Slyke and Hiller 1 and Van Slyke and Robson 2 have reported the presence in gelatin of a new amino acid which is precipitable by phosphotungstic acid. On the basis of the elementary analysis of the copper salt, a positive test for a pyrrol group, and the ratio of amino to total nitrogen, the product was considered as being probably dihydroxy-pyrrol-alanine. According to the criteria which have been suggested by Vickery and Schmidt; 3 the evidence brought out by Van Slyke and his coworkers is not sufficient to consider this substance as one of the accepted amino acids. The experiments herein described deal with a number of attempts to isolate and identify the product described by Van Slyke and his coworkers.

Three lots of about 1 kilo each of a good grade of gelatin were treated essentially as described by Van Slyke and his coworkers except that the bulk of the arginine was first removed by means of flavianic acid. On decomposing the phosphotungstic acid precipitate a product was obtained which was extremely soluble in water but no evidence was obtained to the effect that this substance was dihydroxy-pyrrol-alanine. In the first experiment there was present in this fraction 884 mg. of nitrogen of which 340 mg. were liberated by treatment with nitrous acid in 3 minutes and 374 mg. in 30 minutes. Flavianic acid gave no precipitate with a fairly concentrated solution even on standing for 24 hours at 0°. The substance represented by the amino nitrogen was almost quantitatively precipitated by rufianic acid and by picrolonic acid. The rufianate was amorphous and decomposed without melting. The picrolonate was crystalline and fractional recrystallization from water and dilute alcohol resolved it into at least 3 fractions which differed widely in melting point, solubility, and somewhat in crystal form. None of these fractions could be isolated in pure form.