Chemistry and Biology of Proteins - F. Haurowitz 1953

Albumins, globulins, and other soluble proteins
Protamines and histones

Protamines are relatively simple, low-molecular-weight Proteins with strongly pronounced basic properties. They were first discovered in 1874 in salmon sperm and were subsequently isolated from the sperm of other fish species as well. Protamines occur in sperm as nucleic acid salts and can be obtained in free form by treating dried and defatted sperm with sulfuric acid or copper chloride [176]. They are precipitated from sulfuric acid solutions by picric acid. The most extensively studied protamines include salmine from salmon sperm, clupeine from herring sperm (Clupea harengus), sturine from sturgeon sperm (Acipenser sturio), and scombrine from mackerel sperm (Scomber scomber).

¹ According to M. S. Reznichenko (Biokhimiya, 16, 579, 1951), the length of peptide chains in gliadin ranges from octa- to nonapeptide dimensions. The author suggests that gliadin consists of 25 peptide chains and possesses 25 free terminal amino groups. — Ed. note.

Salmine has a very simple composition. Its molecule contains only seven Different types of Amino Acids, with Arginine predominating. The Molecular Weight of salmine is 8,000; its composition can be expressed by the following formula: arg₄₀, ser₇, pro₄, gly₃, val₂, isoleu₁, ala₁ [177]. Since salmine contains no free amino groups, it can be assumed to be either a cyclopeptide or a peptide whose terminal groups are represented by the imino acid Proline [177]. The Structure of other protamines is more complex than that of salmine. Protamine from sardine sperm contains 15.8% arginine, 15.7% Histidine, 1.09% Tyrosine, and 0.87% Tryptophan [178].

The strongly pronounced Basic Properties of protamines are due to their high arginine content. According to Kossel, later confirmed by other investigators, arginine accounts for approximately ²/₃ of all amino acids in protamines [179–182]. The basic character of protamines is so pronounced that they can combine with atmospheric carbon dioxide to form carbonates. With sulfuric acid, protamines form neutral salts that are soluble in hot Water but separate from the water as an oily layer upon cooling. Salmine and clupeine [183] lack free amino groups, and their terminal carboxyl group belongs to arginine [182].

Histones are also proteins possessing basic properties. These proteins were discovered by Kossel [184] in Cell nuclei, where they are bound to Nucleic Acids. The basic character is less pronounced in histones than in protamines, which is why they are not precipitated by alkaline picrate solutions. Histones may be precursors of protamines, as they have been found in the Testes of immature fish. Due to their alkaline nature, histones are precipitated from solutions by ammonia at their isoelectric point (around pH 8.5), a property utilized in their isolation. The histone from the Thymus gland has been studied in the greatest detail. To obtain this histone, crushed thymus gland tissue is extracted with water, after which acetic acid is added to the aqueous extract. This precipitates nucleohistone, which is then dissolved in alkali. Nucleic acids are removed by precipitation with sulfuric acid, and the resulting histone sulfate is precipitated from the filtrate with ethyl alcohol [185]. Histones have a higher molecular weight than protamines, and their Amino Acid Composition is closer to that of true proteins. They contain Phenylalanine and Tyrosine, as well as small amounts of histidine and Lysine. Histones can be distinguished from protamines by their tyrosine content. To differentiate nucleohistones from true Nucleoproteins, the tryptophan reaction was proposed, since Kossel found that histones contain a small amount of tryptophan; however, according to later studies by Stedman, tryptophan is absent in both thymus and cod sperm histones [186].

Globin—the protein component of Hemoglobin—was at one time classified among histones because, like histones, it precipitates from solution upon The addition of ammonia; however, it was later shown that the preparations investigated contained denatured globin. Native globin is not precipitated by ammonia. Globin also differs from typical histones in its amino acid composition.

Proteins possessing a basic character and occupying an intermediate position in their properties between protamines and histones have been isolated from the sperm of invertebrates; arginine nitrogen accounts for 28% to 83% of the total nitrogen in these proteins [187].