Nutritional efficiency of alpha-ketoisocaproate relative to leucine, assessed isotopically.
The efficiency of alpha-ketoisocaproate as a dietary substitute for leucine was assessed in rats by two techniques: first, the minimal dose of alpha-ketoisocaproate required, as a supplement to a leucine-free diet, to achieve a growth rate as great as animals receiving leucine was found to be between 2.2 and 4.4 times larger. Therefore the nutritional efficiency of alpha-ketoisocaproate lies between 0.23 and 0.46. Second, alpha-[1-14C]-ketoisocaproate and [3H]leucine were administered orally and the ratio of 14C/3H incorporated into the leucine of whole-body protein and fibrin was measured. This ratio, divided by the ratio 14C/3H injected, was the same in fibrin as in whole-body protein and averaged 0.39. Thus both techniques yield the same value, within the error of measurement, for the relative nutritional efficiency of alpha-ketoisocaproate. We also found that alpha-ketoisocaproate feeding at varying dosage did not alter this ratio in whole-body protein (measured in rats fasted overnight), suggesting that neither wide variations in growth rate nor exposure for 10 days to alpha-ketoisocaproate (in a diet of constant protein content) alters the relative rates of utilization (or oxidation) of alpha-ketoisocaproate vs. leucine.
D000818:Animals; D001835:Body Weight / Q000187:drug effects; D002250:Carbon Radioisotopes; D004032:Diet; D004305:Dose-Response Relationship, Drug; D004435:Eating / Q000187:drug effects; D005337:Fibrin / Q000378:metabolism; D007651:Keto Acids / Q000494:pharmacology*; D007930:Leucine / Q000494:pharmacology*; D008297:Male; D009747:Nutritional Physiological Phenomena / Q000187:drug effects*; D014176:Protein Biosynthesis; D051381:Rats / Q000254:growth & development; D011919:Rats, Inbred Strains; D014316:Tritium
D002250:Carbon Radioisotopes; D007651:Keto Acids; D014316:Tritium; C013082:alpha-ketoisocaproic acid; D005337:Fibrin; D007930:Leucine