The Biuret Reaction and the Cold Nitric Acid Test in the Recognition of Protein
Toronto). '(0///1/1 Waled b1 -Francisif. Gooldbo(ly, .LD., 1I.R.C.P. erom tMe Piat/hologieal (Chcwiistry, I)epartnicuit, Unlirersity College1, Lou don. (leieciud IWcbriri y 9th" 1909) Int all books ont physiological chemistry anid clinical diagnosis oiie is recommended to pl1a( e greait relianice oni the biur-et reaetion. In thle course of soiue investigations oni tlhe coniparative reliabilitv of variioIus tests for serumiii albtumient I found(I that I obtainied very colntradictory results
... ictory results witlh this test, adli(therefor-e I thiniik it wi-oul(l be of ilnterest to grive tlhe results wi-hihel I obtainied in an exhaustive series of tests. Thlie uisual mIlethio(d , iveii in books for carrvincr out this test is: thlat onie adds to the albumiieni solution somiie sodal. solutioln .and thleln, drIop by dirop, a very (lilute soluttioni of copper suilplhate, a blue precipitate appealrinig wlhichl, oIn shakiilg, dissolves witlh a piiik tilnge, finally clialnging to a re(ldishl violet.1 Butit on doing(, this I founiid that onie could niot be certaini of obtainin(g the reactioni in a uirinie wliichi by otlher tests, such as cold nitric acid, acetic acid aiid heat, and potatssi3ium ferroevatnide aniid acetic acid, gave clear inidicationis of the presenice of albumienl. It was tlierefore necessary to im.ake up a solutioni containing a definiite (Itialtitv of serum albumiieni and to repeat the tests. Oni doing this I found th.at it was impossible to m.lake certain of obt;aining conistalnt ressults unless onie used solutions of soda anid copper sulplate of defillite strenlgtlh, for tlle additionl of the soda solutioni in varyiilng amountiits made a great differenee in tlhe result of the test. It is genierally recognised tlhzat it is necessary to add a dilutte solutioni of copper sulplhate, anid I founiid tliat' although with a hiigh percelntaghe of albumen a 2;1, per ceint. soluitioni of copper sull)llate iua4 be used, yet for all practical purposes tlhe soluttioni of col)l)pe stulplhate slhotul(d niot be stronger tlhani 1 per centt. Anothel poinit oni which the various text-books, wbhiel I hiave had an opportunity of consultincg, lay little stress is oni that of lheatinig, and 1. Somie text boolos advise adding the copper sulpliate solution before the soda solution.