The discovery of biochemical mutants of Neurospora by Beadle and Tatuni in 1941 afforded some interesting approaches to the problems of growth. One of these approaches involves the relation of genes to the synthesis of the specific vitamins or amino acids which these mutant strains require for growth but are unable to produce (Tatum and Beadle, '42; Bonner, Tatum and Beadle, '43). Another approach concerns the relation of these vitamins and amino acids to growth. In all probability, pyridoxin, pantothenic acid and p-amirio benzoic acid, like thiamin, riboflavin and nicotinic acid, play a role in the action of respiratory enzymes in Neurospora (Giese and Tatum, '42). It follows that the effect on growth of a gene concerned with the synthesis of a growth factor may be through the respiratory system with which the vitamin is concerned.
It therefore becomes desirable to know the relation of particular respiratory systems to growth processes in Neurospora. That a close connection between growth and respiration exists is known, for the mold will not grow in the absence of oxygen. It is the purpose of this investigation to examine the relation between growth and the fourcarbon dicarboxylic acid respiratory system in Neuropsora by studying the inhibition of growth and respiration by iodoacetic acid and the reversal of this inhibition by four-carbon dicarboxylic acids. This approach is based upon the fundamental work of Commoner and Thimann ( '41) who showed that growth of the Avena coleoptile can depend upon the activity of four-carbon dicarboxylic acids.