Amino acid genetic variant

Electrophoresis as a method of study of molecular differences has its limitations. It can demonstrate variation of the primary structure only if it changes migration in the electric field, which is the case only for a fraction (about one third) of the conceivable variants the others are electrophoretically silent. On the other hand, different amino acid replacements may cause the same electrophoretic variant and thus be indistinguishable. Furthermore, the whole method was applicable only to selected types of proteins and could not yield a genetically satisfactory overview. 

K Schmid. Human plasma a,-acid glycoprotein—biochemical properties, the amino acid sequence and the structure of carbohydrate moiety, variants and polymorphism. In P Baumann, CB Eap, WE Muller, JP Tillement, eds. Al-pharacid glycoprotein genetics, biochemistry, physiological function, and pharmacology. Alan R. Liss, New York, 1989, pp 7-22. 

The third relatively well-characterized genetic polymorphism is that of CYP2C9. Two well-characterized variants of this enzyme exist, each with amino acid mutations that result in altered metabolism. The CYP2C9 2 allele encodes an Argl44Cys mutation, exhibiting impaired functional interactions with P450 reductase. The other allelic variant,... 

Amino acid composition. The approximate amino acid composition of the main caseins is shown in Table 4.4. Amino acid substitutions in the principal genetic variants can be deduced from the primary structures (Figures 4.9-4.12). Four features of the amino acid profile are noteworthy ... 

Figure 4.9 Amino acid sequence of bovine atl -casein, showing the amino acid substitutions or deletions in the principal genetic variants (from Swaisgood, 1992).

The division of function between DNA (genetic information storage) and protein (catalysis) was, according to the RNA world hypothesis, a later development. New variants of self-replicating RNA molecules developed, with the additional ability to catalyze the condensation of amino acids into peptides. Occasionally, the peptide (s) thus formed would reinforce the self-replicating ability of the RNA, and the pair—RNA... 

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