The chemistry of heparin

HEPARIN, the anticoagulant discovered by Howell 1918, has not until recent times been readily accessible either to the research chemist or to the physiologist.Its high price has prevented a thorough study of its chemical properties and its more extensive use in physiological laboratories and in clinical practice.Thanks to the recent work of Charles and Scott 1933, fresh possibilities have been afforded in both directions.Heparin has been shown to be a common tissue constituent, and the method of its preparation has been greatly improved.As to the chemical nature of heparin, very little is known.Howell 1928 found a hexuronic acid in his purest preparations.Schmitz and Fischer 1933 described highly purified preparations, which they believed to consist of a trisaccharide, C18H320.7, containing one carboxylic group.Charles and Scott found a positive oa-naphthol reaction, but the test for hexuronic acids with naphthoresorcinol was negative.Consequently the authors agree only in one respect, namely as to the occurrence of carbohydrate groups in the heparin pre- parations.Furthermore, there is disagreement as to the nitrogen content of the preparations.Howell found at an early stage of the preparation that the sodium cyanide test of Lassaigne proved negative, and he gives no further information as to the nitrogen content.Nor do Schmitz and Fischer pay any attention to this question.On the contrary Charles and Scott found about 2 % of nitrogen in their purest preparations, which were as pure as any hitherto prepared.Another finding in the papers of these investigators is also remarkable, namely the high ash content of the heparin samples.Howell found 37 % and Charles and Scott about the same figure.Schmitz and Fischer, who found a certain amount of ash even in the crystalline brucine salt, repeatedly discuss the possi- bility of molecular combination between heparin and neutral salts.This divergence of opinion as to the composition of heparin preparations seemed to justify a reinvestigation.The author therefore prepared heparin from ox and horse liver, following the principles outlined by Charles and Scott.Only in some details was their technique modified.The crude material obtained after tryptic digestion proved to be 2 or 3 times more active than the commercial preparations.After treatment with Lloyd's reagent 2 or 3 times as recom- mended by Howell, no considerable further purification seemed possible.Several attempts to fractionate the preparations with barium acetate, barium hydroxide, lead acetate (basic) and glacial acetic acid did not result in more active products.In this state of purity the samples did not precipitate in aqueous solution with lead acetate or with cadmium chloride.As further purification seemed im- possible, the samples were submitted to analysis.Analysis of the heparin preparations.The different preparations of heparin seemed to be of a rather uniform chemical composition (see Tables I andII).Furthermore the content of ash, 38-41 %, and of nitrogen, 1-63-1'84 %, corresponded with the figures given by Charles and Scott.