Gross protein value

Digestible protein figures are not entirely satisfactory measures of the value of a protein to an animal, because the efficiency with which the absorbed protein is used differs considerably from one source to another. In order to allow for such differences, methods for evaluating proteins, such as the protein efficiency ratio (PER), the net protein retention (NPR) and the gross protein value (GPV), which are based on the growth response of experimental animals to the protein under consideration, have been devised. 

The gross protein value is probably the most commonly used biological method for evaluating proteins. Gross protein values measure the ability of proteins to supplement diets consisting largely of cereals and they correlate well with FDNB-reactive lysine figures. 

Standardised methods (protein efficiency ratio, net protein ratio and gross protein value) based on the growth response of experimental animals are used to evaluate protein sources for monogastric animals. 

Determination of available lysine by reaction of fluoro-4-di nitrobenzene with the reactive epsilon group has been shown to correlate well with gross protein values of animal foods and for supplements for high-cereal diets. 

Source Biological value (rat) Chemical score Protein efficiency ratio (rat) Gross protein value (chick)... 

Data obtained from a national scientific research project entitled Energy and protein value of diets for ruminants , were organized and statistically analysed (ANOVA) to point out differences in energy (NE, Mcal/kg dry matter) and protein (NP, NP/GP, net protein/gross protein) efficiencies values of lucerne hay (Lh) and wheat straw (Ws) in diets for lambs. 

Kauzmann lists some —A//and —AS values for denaturation. Their range is 60-150 kcal/mole and 200-400 e.u. for several proteins. The entropy change is very large, hence denaturation involves a gross gain of entropy in a series of many small increments. In many instances the molecule cannot return to the previous orderly arrangement, and irreversible denaturation is observed. 

Such a procedure adapted from Gross and Morell (1966) and Blumenfeld and Gallop (1962) is as follows. Visser et al. (1971) treated 2.5 to 10 mg of a modified elastase with 1 N NHjOH-HCl, adjusted to pH 9 by addition of sodium hydroxide, for 2 hr at 25°C. The excess hydroxylamine was removed either by dialysis or by precipitation of the protein at pH 3.0. The protein was then dissolved, brought to pH 8.0 by addition of NaOH and treated with an equal volume of a 1 % solution of l-fluoro-2,4-dinitrobenzene in ethanol. The pH of the solution was maintained at 8 by the continuous addition of NaOH. The reaction is complete when no additional alkali must be added for 5 min. The mixture is then extracted three times with ether and the aqueous phase subjected to the conditions of the Lossen rearrangement (i.e. heating to 100°C under alkaline condition (0.1 N NaOH) for 10 min). Acid hydrolysis followed by amino acid analysis permits the identification of either diaminopropionic or diaminobutyric acid which would result from either aspartate or glutamate modification, respectively. Diaminopropionic and diaminobutyric acids may be estimated on the short column of the amino acid analyzer. Diaminopropionic acid emerges with histidine. (Color values do not seem to be available.)... 

Monteagudo C, Merino MJ, LaPorte N, et al. Value of gross cystic disease fluid protein-15 in distinguishing metastatic breast carcinomas among poorly differentiated neoplasms involving the ovary. Hum Pathol. 1991 22 368-372. 

In the absence of titration data for accurate Ap and An values, in the absence of corrections to activities (see above), and without direct calorimetry data to estimate AH, for the specific salt and model protein systems of interest, gross comparison derives from the AGiiA(salt) values listed in Table 5.4A, as determined in section 5.3.4. 

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