Glycine incorporation into tissue proteins

Collagen constitutes 20-25% of the total protein in mammals. Table 12.6 shows data on its amino acid composition. The high contents of glycine and proline and the occurrence of 4-hydro-xyproline and 5-hydroxy lysine are characteristic. Since the occurrence of hydroxyproline is confined to connective tissue, its determination may provide quantitative data on the extent of connective tissue incorporation into a meat product. 

Insulin in vitro increases the recovery of glucose carbon in the trichloroacetic acid-precipitable protein of epididymal adipose tissue from fasted rats (Herrera and Renold, 1960 Carruthers and Winegrad, 1961), and also increases the incorporation of glucose carbon into the ribonucleic acid fraction of adipose tissue from fasted rats (Carruthers and Winegrad, 1962). That these latter effects were observed in the presence of unlabeled glycine suggests that the bulk of the incorporation was into the pento.se moiety. When adipo.se ti.ssue from fasted rats is incubated with pyruvate- -C pyruvate carbon is isolated in the ribonucleic acid fraction however, the addition of insulin does not affect this incorporation (Carruthers and Winegrad, 1962). 

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