Quantitative Aminosäureanalysen und Elektropherogramme zur Frage der identischen Reproduktion des Caseins

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Abstract
The existence of the genetic variants A, B, C and D of as-casein, and A, B and C of 0-caseln has lent support to the concept that an invariable mechanism is responsible for the biochemical replication of this protein. On this basis, changes in the amino acid pattern, brought about by external factors, are generally attributed to changes in the relative proportions of the different protein components (or, [beta]-, gamma- and ?t-casein). Analysis of the casein components by free electrophoresis shows that this explanation is untenable. The average stoichiometric composition is OQj34gammai*3 and the limits of variation are ofg/35gammao-3 and a[beta]2gammaix3. The observedvariationsinthe amino acid composition of the total protein, however, show a much wider scatter than those expected from analysis of the purified components and their recombination in synthetic mixtures corresponding to those shown above. Thus the seasonal variation in the amino acid composition of casein cannot be explained on the basis of changes in the proportions of the components. This led to the isolation of metabolic variants, which are characterized by the changes: Thr3Ser2Glug Thr6Ser3Glu2 and ASP3GIU5[long dash][forward arrow] Asp2Glug in the glycomacropeptide fraction of the casein. These results can be explained by a very wide variation in the specificity of the messenger.

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