Picric acid can be reduced enzymatically into picramic acid. It is conceivable that picric acid accepts hydrogen through flavotprotein.
Yellow picric acid can be converted into red picramic acid by whole cells and cell-free preparations under aerobic conditions. Picric acid appears to be utilizable as a redox dye.
The author wishes to express his appreciation to Dr. R. Katsunuma, director of the Obuso National Sanatorium, Prof. S. Hibino, Nagoya University, and Prof. N. Katsunuma, Osaka University, for their kind encouragement and advice. The author is also indebted to Mr. S. Mizuno for his technical assistance.
