Abstract
The work reported was originally an attempt to follow free cystine in blood by means of the Folin-Looney 1 , 2 method. It was planned, if possible, to repeat with cystine the work done in this laboratory with tryptophane 3 , 4 and thus to follow its utilization by the mammary gland in milk secretion, and to study further the changes that may occur in the composition of the blood mixture of amino acids as a result of various changes in diet.
Protein free blood extracts were made as in the amino N determinations in this laboratory. 5 , 6 These extracts gave values with the Folin-Looney method equivalent to 4 to 7 milligrams of cystine per 100 cc. of blood, and 85 per cent of this occurred in the corpuscles. This was much higher than expected. Further-more, when cystine was added to the original blood it was never recovered quantitatively. Of 4 mg. dissolved in the acetic acid to be used in the coagulation of the blood, only 1.36 mg. were recovered. When 100 cc. of the original blood were shaken for half an hour with 100 mg. of cystine, only 5 mg. were recovered. With the Folin and Wu 6 tungstic acid method larger amounts of this color producing substance were found in the blood, but there was no recovery of added cystine. Passing air or hydrogen sulphide through the blood for three hours before coagulation had no effect upon the color given by it or upon the recovery of added cystine. Other methods of deproteinization were tried. The results indicated that the color-producing substance in the blood was not cystine; although, when heated with alkali and lead acetate, it gave a precipitate of lead sulfide, and, after treatment with mild reducing agents, it gave the nitroprusside test.
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