Studies on the purification of collagen

Abstract

Several methods of purifying collagen were studied. The effects of particular treatments on collagen were followed by nitrogen determina tions, by electrometric t itra tion analyses, and by electrophor etic measurements. Treatment of the raw material with t rypsin , as in the conventional method for t he preparation of collagen, results in changes t hat lead to a degradation of the collagen in s ub-sequent extr actions. Treatment with dilu te salt solut ion followed by trypsin produces a rpa-terial of compal'ati vely low isoelectic point (pH 5.5). Apparently soakin g in dilute salt solu t ion is not detrimental to collagen, and it is r ecommended that this type of extraction be sub tituted for t he extraction with trypsin. A technique for removing all but a negligible part of the mineral content from collagen is described, and a pr ocedure is recommended for use in the preparation of ash-free gelatin. A specification is proposed for purified collagen: (1) The water extract shall have a pH range of 6.0 to 7.0 ; (2) the isoelectric point (determined electrophoretioally) shall be between pH 6.0 and 7.5; (3) the material shall have an ash content of less than 0.1 percent, total nitrogen content of 17.8 to 18.1 percent, and au amide nitrogen content (determined by hydrolyzing for 20 hours in 0.1 N hydrochloric acid at 90° C) of at least 3.8 perccnt, expre1'sed as perce ntage of total nitrogen.