Histones

Histones, basic proteins, were first isolated by Kossel from the red blood cells of goose blood. They occupy an intermediate position between protamines and native proteins. They contain 16.5-19.8% nitrogen; up to 40% of this belongs to hexone bases (see). The nitrogen of arginine constitutes 12-20%, lysine 7-8.5%, and histidine 1.2-4.5% of the total nitrogen. Along with basic N, unlike protamines, histones contain a considerable amount of monoamino acids and apparently firmly bound sulfur. They give biuret and Millon reactions. They are insoluble in water, but readily dissolve in acids. Like protamines, they are precipitated by alkaloidal reagents without acidification and cause protein precipitation. When digested with pepsin, they yield a histopectin rich in arginine. A neutral, salt-free solution of goose blood histones is characterized by the following properties: 1) it does not coagulate when boiled, 2) it is insoluble in NH₃ in the presence of ammonium salts, 3) nitric acid gives a precipitate that dissolves upon heating and reappears upon cooling. Histones are found in the tissues and organs of humans and some animals in the form of salt-like compounds with acid-reacting substances, for example: thyroid nucleohistone (histone+nucleic acid), hemoglobin (globin+heme), etc. They have also been found in the spermatozoa of mackerel (scombron), cod (gadushistone), tadpole (lotahistone), and sea urchin (arbacin).