Endogenic fractions

In conclusion.TMEn is the best estimation of the metabolisable energy of a diet because it is independent of the level of ingestion and does not into account the endogenous fraction that does not come directly from the diet Theoretically, only TMEn values are additive However, when ingestion levels are close to spontaneous ingestion levels in the birds, AMEn and TMEn are similar. 

Now and again doubt arose Key s (1895) and other experiments did not go very deeply into the problem, and new studies were performed. Nicolaysen was the first to explore the problem fully (1934) and to reach a conclusive result. As the poorly founded postulate of active re-excretion and secretory function of the colon is again being given consideration, a brief summary of Nicolaysen s (1934) experiments will not be out of place. The argument was comparatively simple, namely that the endogenous fraction of the fecal calcium could not be studied except on a diet free of calcium. 

This is a direct measure of the proportion of the food protein that can be utilised by the animal for synthesising body tissues and compounds, and may be defined as the proportion of the absorbed nitrogen that is retained by the body. A balance trial is conducted in which nitrogen intake and urinary and faecal excretions of nitrogen are measured, along with the endogenous fractions in these two materials. The biological value is then calculated as follows ... 

The endogenous urinary nitrogen results from irreversible reactions involved in the breakdown and replacement of various protein secretions and structures within the body. Thus, both the faecal and urinary endogenous fractions represent nitrogen that has been absorbed and utilised by the animal rather than nitrogen that cannot be so utilised. Their exclusion from the faecal and urinary values in the above formula gives a measure of the true biological value. 

Because the protein analyte is endogenous to the plant, it can be difficult to demonstrate the efficiency of the extraction procedure. Ideally, an alternative detection method (e.g., Western blotting) is used for comparison with the immunoassay results. Another approach to addressing extraction efficiency is to demonstrate the recovery of each type of protein analyte from each type of food fraction by exhaustive extraction, i.e., repeatedly extracting the sample until no more of the protein is detected. " ... 

Supernatants were chromatographed over a column of Sephadex G-10, G-25, and G-50, and aliquots of collected fractions were assessed for their ability to displace 3H-PCP from binding sites in rat brain preparations. Results indicated that the endogenous material has a molecule weight of about 3,000. 

FIGURE 2. Panel A Elution pattern of endogenous PCP-like material from fractionated porcine brain. Activity is expressed in terms of equivalents of PCP required to inhibit 3H-PCP bindina to rat brain membranes. One unit of activity is eqivalent to 1 mole of PCP. 

A further promising attempt to identify the bluelight-reducible cyt b is described by Britz et al.26) for a plasma-membrane-enriched fraction of com coleoptiles. They find that methylene blue (Scheme 2) is capable of reducing a particular cyt b which constitutes only 10—20% of the total dithionite-reducible cytochromes. Since this particular cyt b is very similar to that which is photo-reduced by endogeneous flavin in Neurospora 122,123) the two are proposed to be identical. 

---