Lysinoalanine lactalbumin

Metabolic Transit of Lysinoalanine. Urinary and Fecal Excretion of Protein-Bound Lysinoalanine (113). Three different alkali-treated proteins (lactalbumin, fish protein isolate, and soya protein isolate) containing, respectively, 1.79, 0.38, and 0.14 g of lysinoalanine/16 g nitrogen were given to rats and the urines and feces were collected. Lysinoalanine was measured before and after acid hydrolysis. The fecal excretion varied from 33 to 51% of the total ingested lysinoalanine and the urinary excretion varied from 10 to 25%. The higher level of lysinoalanine found after acid hydrolysis indicates that a certain quantity is excreted in the urines as combined lysinoalanine (see Table VII). The total recovery was inferior to the ingested quantity (50 to 71%) indicating that the molecule is transformed or retained in the body of the rat. 

Comparison of lysinoalanine values for wheat gluten, casein and lactalbumin treated at various pH s shows large differences in the amounts of lysinoalanine formed in the three proteins. 

For example, the respective values at pH 10.6 are 0.262, 0.494, and 1.04 mole per cent (ratio of about 1 2 4) at pH 11.2 the values are 0.420, 0.780, and 1.32 mole per cent and at pH 12.5 (pH of 1% protein solution in 0.IN NaOH), the respective values are 0.762, 0.780, and 2.62 mole per cent. (Note that the value of casein approaches that of gluten at this pH). The observed differences in lysinoalanine content of the three proteins at different pH values are not surprising since the amino acid composition, sequence, protein conformation, molecular weights of protein chains, initial formation of intra- versus intermolecular crosslinks may all influence the chemical reactivity of a particular protein with alkali. Therefore, it is not surprising to find differences in lysinoalanine content in different proteins treated under similar conditions. These observations could have practical benefits since, for example, the lower lysinoalanine content of casein compared to lactalbumin treated under the same conditions suggests that casein is preferable to lactalbumin in foods requiring alkali-treatment. 

Lysinoalanine formation in casein, lactalbumin, and wheat gluten was measured at 65°C at various pH s for 3 hours. Factors that control the extent of formation of the unnatural amino acid lysinoalanine during food processing and thus the degree of crosslinking in structurally different proteins are discussed. 

Figure 1 summarizes the potential pathways involved in the formation of dehydroalanine. It appears that dehydroalanine can be formed in a variety of amino acids protein, suggesting that any or all of the routes in Figure 1 could be involved in dehydroalanine formation. Table 1 contains results of partial amino acid analysis of several alkaline treated proteins. The results support the suggestion that both serine and cystine or their derivatives can be sources of dehydroalanine and subsequently the lysinoalanine measured in the proteins. In casein there is substantial LAL formation with a measurable loss in serine. In isolated soy protein and lactalbumin it can be seen that cystine shows the most significant losses. It should be noted that a significant portion of the serine in casein is present as phosphoserine. The relatively rapid 6-elimination of phosphoserine (15) accounts for the formation of considerable quantities of dehydroalanine and subsequently the substantial levels of LAL found in casein. In addition, as mentioned above, the presence of calcium would accelerate dehydroalanine formation from the phosphoserine present in the casein. The variability of... 

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