The kinetics of the reduction of riboflavin by dithionite

1. I. The reduction of riboflavin by dithionite was followed, using a rapid mixing apparatus, over a range of concentration, acidity and temperature. 2. 2. The time-course of reduction of riboflavin in the presence of excess dithionite was found not to be of exponential form, but of approximately linear form. Evidently the reaction is complex. 3. 3. In sufficiently dilute riboflavin solutions, the initial reaction velocity was directly proportional to riboflavin concentration. Under these conditions, the Q 10 was approximately 2.0. 4. 4. In sufficiently concentrated riboflavin solutions, the initial reaction velocity became nearly independent of riboflavin concentration. 5. 5. An intermediate was found by its absorption in the infra-red. The maximum amount of intermediate formed was proportional to the square of the riboflavin concentration. The intermediate was only detected in sufficiently concentrated riboflavin solutions. Smaller amounts of intermediate were formed at higher temperatures. 6. 6. The mechanism of the reaction is discussed.