Сельскохозяйственная биология, 2010, № 4, с. 73-77.

УДК 636.93:591.3:[591.176+591.478.1]:577.112.5

AGE-SPECIFIC CHANGES IN AMINO ACIDS COMPOSITION OF SKIN AND FUR IN MINKS AND FOXES

I.N. Staroverova

The amino acid composition in proteins of skin and fur was studied in standard minks and silvery-black foxes on different stages of their ontogenesis. It was established, that the skin in mink and fox has similar composition, depending on age. The biochemical composition of fur in fur-bearing animal changes less considerably and depends on morphological structure of hair.

Key words: silver-black foxes, mink, ontogenesis, hair, skin, amino acids composition.

The study of amino acid composition in skin of fur-bearing animals is of great theoretical and practical interest, owing to the fact that skin provides a formation of valuable proteinaceous product - fur. The study of age dynamics in this characteristic of skin and fur is important for identifying the specific ontogeny features used as a biological basis for zootechnical activities developed in fur farms. The amino acid composition of skin and fur was studied in sheep, goats and seals (1-4). Thus, it has been shown that a fur of sheep and goats has close amino acid composition, whereas in seals, the content of valin is about 10 times, lysine - 4, histidine - 3, alanine and arginine – 2 times higher, and glycine - 2 times lower (1, 3, 4). In sheep, the content in skin of cysteine, histidine, lysine, arginine and alanine is higher than that of seal (1-3). At the same time, no analogical data on fur-bearing animals were found in the available scientific literature.

The purpose of this study was to compare the amino acid composition of proteins in skin and fur of standard minks and silver-black foxes in different periods of their ontogeny.

Technique. The objects of research (2007-2008) were the males of silver-black fox and standard mink kept in the breeder-farm Plemzavod “Saltykovsky” (Moscow province). Animals’ diets and housing conditions corresponded to the established norms.

The amino acid composition of fur and skin were analyzed in 30- and 90-days old animals, in 7-month-old animals with completely formed winter fur and in 1-year-old animals during the spring molt. The tested animals were taken from healthy mothers who had been fed with full-nutrition diets during a pregnancy and lactation. The studies were carried out in 4-fold replication upon three individuals from each age group. Sampling, preparation (5), acid hydrolysis (6) and amino acid analysis of samples were performed using the device Amino Acid Analyzer A0326 (“KNA-UER”, Germany). Separation of free amino acids was performed on sulfocationite with post – column derivatization with ninhydrin (7).

Results were statistically processed in the program ClarityChrom ® V2.6.5.

Results. It has been found, that skin proteins of standard minks contain significant amounts of glycine, glutamic acid, aspartic acid, lysine, serine, threonine, alanine, leucine and arginine; in fur keratin - serine, glutamate, ascorbic acid, glycine, valine, arginine, lysine, threonine, aspartic acid, leucine, alanine and methionine were detected. The remaining amino acids were found in content less than 3% (Table). Between the age groups, the content in skin of arginine varied by less than 71,3 %, threonine – 52,2, leucine – 43,2, glycine – 32,8, aspartic acid – 24,8, alanine - 23,6 , serine – 23,0, lysine – 22,4, glutamic acid - 13,9% (total sum of amino acids - no more than by 1,0%). The content of glycine in fur keratin varied in animals of different ages by less than 34,0, aspartic acid – 32,2, arginine - 30,6, alanine – 26,7, leucine - 20,8, threonine - 15,5, lysine - 12,7, glutamic acid - 10,1, serine - 7,0 (total sum of amino acids - no more than by 14,4%).

Skin proteins significantly differed from fur keratin by their amino acid composition and exceeded it in contents  of amino acids: glycine - in 2,0-3,9 times, proline - in 1,1-1,8, alanine - in 1,2-2,0, aspartic acids - in 1,4-1,6, glutamic acid - in 1,1-1,3 times, but they yielded in contents of methionine - in 1,1-2,0 times, cysteine - in 1,4-12,0, valine - in 2,8-6,6, serine - in 1,4-1,8, tyrosine - in 1,3-2,3, threonine - in 1,1-2,2 times depending on age.

In skin proteins of silver-black foxes, the content of leucine varied in age groups by less than 59,5 %, threonine – 53,6, glycine – 45,3, arginine - at 38,0, aspartic acid - by 30,6, lysine – 27,0, alanine - by 24,9, serine - 22,0, glutamic acid - by 13,0% (total sum of amino acids - no more than by 2,0%);  in fur keratin, the content of alanine - less than by 40,8%, lysine – 39,5, methionine - 34,6, serine - 26,8, threonine - 23,4, valine – 20,8, glycine - 17,4, leucine – 14,0, glutamic acid - 13,9, arginine - 12,8, aspartic acid - by 1,9% (total sum of amino acids - no more than by 8,1%) (See table).

For the foxes, the skin proteins exceeded fur keratin by the content of glycine in 1,7-2,9, alanine – in 1,6-2,7, proline - in 1,2-1,9 times, while the fur keratin exceeded skin proteins in contents of cysteine in 1,2-13,1, valine - in 3,7-10,6, serine - in 1,2-1,9, tyrosine - in 1,5-2,2, threonine - 1,1-2,3 and methionine - in 1,1-1,8 times depending on age.

In both studied species, skin proteins contained more alanine, proline and glycine compared with fur keratin. The age and interspecific differences in amino acid composition of skin proteins were observed for the content of alanine, aspartic acid, serine, glutamic acid, proline - less than in 1,2 times, lysine, phenylalanine, glycine - 1,4; threonine , valine, isoleucine - 1,5, histidine, methionine, tyrosine, - 1,7, arginine, leucine - 3,0, cysteine - in 4,6 times.

For the standard minks, the fur keratin in all age groups contained more cysteine and arginine than that of silver-black foxes. It has been identified the interspecific differences in amino acid composition of fur keratin by the content of valine and serine – in less than 1,2 times, threonine, tyrosine, phenylalanine, lysine, glycine, methionine – in 1,4, proline, glutamic acid, leucine – in 1,5, cysteine, alanine, isoleucine, arginine and aspartic acid – in 1,9 times.

The obtained results were significantly different from the data of literature reports on other species. The comparison of skin proteins of seals and fur-bearing animals has shown that the contents of proline, cysteine, methionine, tyrosine, lysine differed between these species in less than 10 times (1), threonine, serine, arginine, histidine and alanine - in 2,0 - 4.0 times. The fur keratin of minks and foxes contained more than 10 times higher content of valine, 1,5-3,0 more arginine and lysine, 3,0-4,5 times  higher content of serine and methionine compared with corresponding data for; though, the content of cysteine and proline was lower in, respectively more than 3 and about 10 times.

The amino acid composition of skin in sheep (2, 3) and fur-bearing animals were different as well: by cysteine content - in about 20 times; proline, valine - 2,0-5,0, glycine, tyrosine, isoleucine, histidine - 2,0-4, 0, serine, glutamic acid – in 2,0 times. Fur keratin of the studied animals was distinct from the keratin of sheep wool (2, 3) and the goat down (4) by proline content - in 20,0 times; methionine - 4,0-14,0; lysine - 2,0-4,0 ; cysteine - 3,0-10,0; leucine, isoleucine, tyrosine - 1,5-3,0; histidine - in 1,5-2,5 times.

The variations of amino acid composition of skin proteins between age groups and within a species of minks and foxes were found to be more pronounced than those between species. The differences in amino acid composition of skin proteins between 1-month-old animals and other age groups can be explained by a deep reorganization of the dermis and the formation of fibrous structure during the transition from mesenchyme stage to following stages (3). Subsequent changes in the dermis were connected with maturation of collagen, which process was accompanied by increase in fibers density, changes of network patterns and morphological structure of fibrous beams (3). In 7 - and 12-month-old animals, a skin morphostructure was defined by a functional state (rest and molt).

Thus, the amino acid composition of fur keratin proteins in minks and foxes differed to a lesser extent than that of skin. At the same time, in sheep (3), it was weakly dependent on age. Mink fur contains less arginine (in 1,2-1,9 times), but more leucine, isoleucine (in 1,1-1,5 times), cysteine (in 1,2-1,6 times ) compared with foxes. It is known, that the core layer of guard hair is thicker in a fox fur than that in minks (8). The author’s data suggest a relationship between the biochemical composition of fur and its morphological structure in fur-bearing animals. A similar correlation is known for fine-wool and coarse wool sheep (3).

The completely formed (mature) winter fur in the studied animals included the larger set of amino acids compared with spring fur, which fact is apparently explained by the destruction of keratin under environmental conditions. Formation of keratin is completed in hair follicles with no later inclusions into the hair of amino acids (3). After the formation of fur in fur-bearing animals, the gradual destruction of keratin proteins leads to the decrease in content of most of amino acids, whose total quantity reduced by 5,9% in silver-black foxes and by 11,5% in standard minks. This difference is probably associated with the fact that a fox fur is thicker and longer, which gives the better protection from external factors to most part of the fur.

Literature data recommend various approaches for the selection of young animals suitable for breeding work - upon the biochemical indicators of blood serum (9), hormonal activity of thyroid function (10), etc. The author believe that the established differences in amino acid composition of skin proteins and fur, as well as its age-related changes, may be used in addition to known selection criteria and applied for the assessment of physiological state of the fur-bearing animals.

Thus, the skin of standard minks and silver-black foxes has similar amino acid composition, depending on age. Biochemical composition of fur in fur-bearing animals varies considerably less and, apparently, depends on morphological structure of fur. The detected differences in amino acid composition of proteins in skin and fur of Canidae and Mustelidae were found to be less pronounced compared with Pinnipeds and Even-toed ungulates.

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