Proteins dietary protein

Fate of Proteins Dietary proteins are digested to amino acids, which are absorbed into the blood. In cells, the amino acids are converted to proteins or used to make various nitrogen-containing compounds such as neurotransmitters and heme. The carbon skeleton may also be oxidized for energy directly, or converted to glucose. 

The nutritional value of a food is mainly determined by the amount of protein it contains and the quahty of that protein. Dietary protein quahty depends on how well the essential amino acid content... 

Protein. Dietary protein increases the rate of calcium absorption from the small intestine. The probable explanation of this phenomenon is that the amino acids, especially lysine and arginine, liberated in the course of protein digestion, form soluble calcium salts which are easily absorbed. But any advantage from increased absorption will likely be more than counterbalanced by the increas urinary loss of calcium on high-protein diets. 

The mmen is not functional at birth and milk is shunted to the abomasum. One to two weeks after birth, the neonate consumes soHd food if offered. A calf or lamb that is nursing tends to nibble the mother s feed. An alternative method of raising the neonate is to remove it from its mother at a very young age, <1 week. A common example of an early weaning situation is the dairy calf that is removed from the cow soon after birth so that the cow s milk supply might be devoted entirely to production. In this instance, the neonate requires complete dietary supplementation with milk replacer. Sources of milk replacer protein have traditionally included milk protein but may also include soybean proteins, fish protein concentrates, field bean proteins, pea protein concentrates, and yeast protein (4). Information on the digestibiUty of some of these protein sources is available (4). 

Urea Pharmacokinetics. Pharmacokinetics summarizes the relationships between solute generation, solute removal, and concentration in a patient s blood stream. In the context of hemodialysis, this analysis is most readily appHed to urea, which has, as a consequence, become a surrogate for other uremic toxins in the quantitation of therapy and in attempts to describe its adequacy. In the simplest case, a patient is assumed to have no residual renal function. Urea is generated from the breakdown of dietary protein, accumulates in a single pool equivalent to the patient s fluid volume, and is removed uniformly from that pool during hemodialysis. A mass balance around the patient yields the following differential equation ... 

Pepsin Animal stomach Digestion of dietary protein... 

Amide hydrolysis is common in biological chemistry. Just as the hydrolysis of esters is the initial step in the digestion of dietary fats, the hydrolysis of amides is the initial step in the digestion of dietary proteins. The reaction is catalyzed by protease enzymes and occurs by a mechanism almost identical to that we just saw for fat hydrolysis. That is, an initial nucleophilic acyl substitution of an alcohol group in the enzyme on an amide linkage in the protein gives an acyl enzyme intermediate that then undergoes hydrolysis. 

Ambrose, S.H. and Norr, L. 1993 Experimental evidence for the relationship of the carbon isotope ratios ofwhole diet and dietary protein to those ofbone collagen and carbonate. In Lambert, J.B. and Grupe, G., eds.. Prehistoric Human Bone Archaeology at the Molecular Level. Berlin, Springer-Verlag 1-37. 

Gaebler, O.H., Vitti, T.G. and Vukmirovich, R. 1966 Isotope effects in metabolism of N and from unlabeled dietary proteins. CanadianJournal of Biochemistry 44 1249-1257. 

Before proposing a general formulation, we illustrate a DIFF with a simple case, in which we consider bone collagen as the body component, and the diet as containingjust two components, protein and non-protein. In the notation, B stands for body 5 values, and D for diet 8 values suffixes distinguish the particular component specified. Thus Bcolla stands for the collagen 8 C, Dp and Dn for the dietary protein and non-protein 6 C values. 

In words, the DIFF equation states that the observed collagen 8 values are determined by both the dietary protein (with additional isofractionation), and the non-protein in the diet (with a potentially different isofractionation), by an amount that may vary with the fraction of each component in the diet. Note that if dp and dN were both set equal to -i-5%o, and if the f(F) were set = 1, this would re-state the original DIFF you are (i.e., your collagen is) what you eat (protein and non-protein) plus five permil . 

Figure All.l. A plot of the difference (residuals) between observed collagen 5 C values and values calculated from the DIFF for dp = +5, dn = +2, and f(F) = F , as a function of the dietary protein carbon content. Due to the eombination of eomposition and manipulated isotopic compositions of the different diets, some diets test the predictions of the DIFF more precisely than others. These are represented as squares (the remainder are represented as diamonds). Although the differenee has been minimized, it is not zero. Nevertheless, and especially for the more reliable reetangular points, the differenee is small, for a wide range of diets and collagen 8 values. Other combinations of dp, ds. and 1(F) give greater residuals.

Amino acid synthesis in heterotrophs primarily relies on dietary protein rather than on lipids or carbohydrates (Schwarcz, 2000), and thus the isotopic composition of the resulting new collagen is related more to dietary protein rather than to bulk diet. Trophic... 

Boyd EM, Dobos I, Krijnen CJ. 1970. Endosulfan toxicity and dietary protein. Arch Environ Health 21 15-19. 

Tyagi SR, Singh Y, Sriram K, et al. 1985. Quality and quantity of dietary protein and acute endosulfan metabolic toxicity in rat liver microsomes. Indian J Med Res 81 480-487. 

As the name implies, the odor of urine in maple syrup urine disease (brancbed-chain ketonuria) suggests maple symp or burnt sugar. The biochemical defect involves the a-keto acid decarboxylase complex (reaction 2, Figure 30-19). Plasma and urinary levels of leucine, isoleucine, valine, a-keto acids, and a-hydroxy acids (reduced a-keto acids) are elevated. The mechanism of toxicity is unknown. Early diagnosis, especially prior to 1 week of age, employs enzymatic analysis. Prompt replacement of dietary protein by an amino acid mixture that lacks leucine, isoleucine, and valine averts brain damage and early mortality. 

Few peptide bonds that are hydrolyzed by proteolytic enzymes are accessible without prior denaturation of dietary proteins (by heat in cooking and by the action of gastric acid). 

CARMONA A (1996) Tannins thermostable pigments which complex dietary proteins and inhibit digestive enzymes. Latinoam Nutr. 44 31S-35S. 

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