WHOLE-RAT PROTEIN-CONTENT ESTIMATION - APPLICABILITY OF THE N-X-6.25 FACTOR

The amino acid composition of the protein from three strains of rat (W istar, Zucker lean and Zucker obese), subjected to reference and high- fat diets has been used to determine the mean empirical formula, molec ular weight and N content of whole-rat protein. The combined whole pro tein of the rat was uniform for the six experimental groups, containin g an estimate of 17.3% N and a mean aminoacyl residue molecular weight of 103.7 This suggests that the appropriate protein factor for the ca lculation of rat protein from its N content should be 5.77 instead of the classical 6.25. In addition, an estimate of the size of the non-pr otein N mass in the whole rat gave a figure in the range of 5.5% of al l N. The combination of the two calculations gives a protein factor of 5.5 for the conversion of total N into rat protein.