Genetically controlled quantitative variation of ornithine transcarbamylase in the chick kidney

This experiment was made to show that the marked variation in ornithine transcarbamylase (OTC) activity observed within a chicken breed or among breeds is due to quantitative changes, not qualitative ones. The enzyme was partially purified from three different chicken breeds, the White Leghorn B line, the Cochin Bantam breed, and a commercial line named "G," by the following steps: (i) extraction of OTC with Triton X-100 and cetyl-trimethylammonium bromide, (ii) heating, and (iii) salting-out column chromatography. No difference was shown immunologically, enzymologically, or physicochemically among the partially purified OTCs. The enzyme amount determined using anti-bovine OTC antiserum was related linearly to the enzyme activity either from the same chicken breed or from different breeds. These results suggest that marked variation in OTC activity reflects variation in the amount of enzyme synthesized in the kidney, and this is controlled by regulatory genes encoded on an autosome, not the structural gene.