Protein respiratory quotient

This replacement in the mixture of carbohydrate by fat is accompanied by a decline in the non-protein respiratory quotient, and when the theoretical value for fat (0.7) is reached it can be assumed that energy is being obtained only from body reserves. In ruminants, an additional indication that the post-absorptive state has been reached is a decline in methane production (and therefore digestive activity) to a very low level. 

There are no convincing experimental data, based on respiratory quotients, which support the hypothesis that fatty acids are convertible to sugar. Contrasted with the marked alterations which have been observed when carbohydrate is being changed to fat, the decreases in R. Q. below the level of 0.707 for fat, which should be observed if fat were changing to carbohydrate, are very small and can be partially if not entirely explained by alterations in the R. Q. of the metabolized protein and fat, due to their incomplete, oxidation. 

Amitrole had a drastic effect on the fixation of 14C02 by illuminated chloroplasts of Chlorella pyrenaidom, lowering the incorporation into sucrose by 95% at a concentration of 500 mg. per liter it did pot affect phosphorylated compounds.145 Carbohydrates hydrolyzable by acids were higher (51%) in treated, chlorotic corn leaves than in controls (32%), and this result was interpreted as due to increased metabolism of proteins and fats. The respiratory quotient of 0.8 to 0.88, compared to controls near 1.0, supported this interpretation.145... 

It is not yet clear which estimates of the ratio between the levels of protein and of carbohydrate metabolism during hypoxia should be regarded as reliable. It seems likely that the increase in respiratory quotient in freshwater fish to values of 2.5-2.8, as found by Mohamed and Kutty (1983a, 1986), indicates a predominance of protein expenditure over that of carbohydrate. A hypoxic environment shifts the acid-base balance of the fish towards acidosis (Kotsar, 1976), thereby inducing the redistribution of electrolytes, alteration of ion exchange and the activity of Na+-K+-Mg2+-ATPases and alkaline phosphatases. It also leads to an increased level of C02 in the blood, which enhances the bicarbonate buffer system (Kotsar, 1976). In section 2.1, we... 

Insulin is probably the most important inhibitor of lipolysis. In contrast to adults, in whom catecholamines represent the most important stimulators of lipolysis, thyrotropin (TSH) is the most important stimulator of lipolysis in the newborn. Plasma free fatty acid concentrations rise markedly in the first hours after birth in response to a marked increase in the TSH concentration and a fall in the insulin concentration. The fatty acids released from lipid stores are oxidized by some extrahepatic tissues (e.g., heart and skeletal muscle, kidney, intestine, and lung). Because the respiratory quotient (the ratio of carbon dioxide production to oxygen use) falls from a value of 1.0 (showing that carbohydrate oxidation is the primary source of energy) to a value of 0.8 to 0.9 (showing increasing oxidation of protein or fatty acids) at 2 to 12 hours of age, at a time when protein catabolism is usually insignificant, fatty acid oxidation must represent... 

Respiratory Quotient Data from Human Studies 293 Fatty acyl-S-protein -7 =--— HS protein... 

Respiratory Quotient Data from Human Studies Protein Oxidation and the Respiratory Quotient Calculating Energy Expenditures... 

Indirect calorimetry, a technique that measures Oj consumption and COj production, can be used when more accurate determinations are required for hospitalized patients. A portable indirect calorimeter is used to measure oxygen consumption and the respiratory quotient (RQ), which is the ratio of Oj consumed to COj produced. The RQ is 1.00 for individuals oxidizing carbohydrates, 0.83 for protein, and 0.71 for fat. From these values, the daily energy expenditure (DEE) can be determined. 

Animals do not normally obtain energy exclusively from either carbohydrate or fat. They oxidise a mixture of these (and protein). Consequently, in order to apply the appropriate thermal equivalent, it is necessary to know how much of the oxygen is used for oxidation of each nutrient. The proportions are calculated from what is known as the respiratory quotient (RQ).This is the ratio between the volume of carbon... 

In some situations, discussed in more detail later, heat production has to be estimated from oxygen consumption alone. If a respiratory quotient of 0.82 and a thermal equivalent of 20.0 kJ/1 are assumed, then departures from this RQ in the range of 0.7-1.0 cause a maximum bias of no more than 3.5 per cent in the estimate of heat production. A further simplification is possible in respect of protein metabolism. The thermal equivalent of oxygen used for protein oxidation is 18.8 kJ/1, not very different from the value of 20.0 assumed for carbohydrate and fat oxidation. 

The respiratory quotient (RQ) is the volume of carbon dioxide produced divided by the volume of oxygen consumed in the tissues in a given period of time. The value of the RQ depends on the nature of the metabolic energy source. For carbohydrates, the RQ is 1, for fats it is 0.7 and for proteins it is 0.8, A healthy subject on an ordinary mixed diet of carbohydrate, fat and protein has an RQ of typically 0.85. The RQ is of significance in its influence on the difference in pH comparing arterial and venous blood, to be described next. 

The metabolism of proteins gives a ratio of carbon dioxide produced to oxygen consumed that is intermediate between that of carbohydrate and fat - this is because proteins contain relatively more oxygen per carbon than do fats, although less than carbohydrates. For protein metabolism the respiratory quotient = 0.8. The amount of protein being oxidized can be determined quite separately, by measurement of the excretion of urea, the end-product of amino acid metabolism (section 9.3.1.4). 

Measurement of the respiratory quotient and urinary excretion of urea thus permits calculation of the relative amounts of fat, carbohydrate and protein being metabolized. In the fasting state (section 5.3.2), when a relatively large amount of fat is being used as a fuel, the respiratory quotient is around 0.8-0.85 after a meal, when there is more carbohydrate available to be metabolized (section 5.3.1), the respiratory quotient... 

Estimating the average respiratory quotient over the period from the proportions of fat, carbohydrate and protein in the diet and allowing for any changes in body fat permits calculation of the total amount of oxygen that has been consumed, and hence the total energy expenditure over a period of 2—3 weeks. 

Respiratory quotient (RQ) The ratio of carbon dioxide produce to oxygen consumed in the metabolism of metabolic fuels. The RQ for carbohydrates = 1.0, for fats 0.71 and for proteins 0.8. 

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