Figure 14.1A One Gene, One Enzyme

Original Paper: Srb, A. M. and N. H. Horowitz. 1944. The ornithine cycle in Neospora and its genetic control. Journal of Biological Chemistry 154: 129–139.

Srb and Horowitz developed several mutant strains of Neurospora that could not make arginine (arg). Several molecules including ornithine and citrulline are needed for arginine synthesis. By systematically adding each of these molecules to the growth media for the mutant strains, the researchers deduced that each mutant strain was deficient in one enzyme along a biochemical pathway.