It has previously been suggested that enzyme inhibitors such as the urethanes, urea, thiourea, etc., may act by forming complexes with the metal portions of certain enzymes, and especially those which contain copper (Dubois and Erway, '46; Bodine and Fitzgcrald, '49). The formation of such complexes docs not appear in general to have been extensively studied. Complexes of several metals with biuret bave been described bp Jesserer and his co-workers (Lieben and Jesserer, '36a, '36b; and Jesserer, '36).
The following experiments were performed in an attempt to demonstrate the formation of such complexes, both in vitro and vivo.
Reagent grade chemicals were used throughout this study, as was glass-distilled water. The spectrophotometric determinations were made with a Beckman model D. U. quartz spectrophotometer, using cells 1.000 2 3 ern deep, and a spectral band width of 1.2 mp. The pure solvent of the compound under study was used as a reference in all cases.
If a 0.25M solution of cupric acetate is made 0.535 with respect to thiourea, a dense brown precipitate appears which is only sparingly soluble in water and is readily collected by filtration. The filtrate appears as a clear, green solution. Figure IAided by a grant froni the National Institute of Health.