Abstract
Escherichia coli B/r cells grown on glycerol-containing medium and irradiated with ultraviolet light to about 1% survival respire for about 1 hr and then cease completely for several hours. The results of studies on cell-free respiration and analyses of pyridine nucleotide levels at various times after ultraviolet irradiation show that the cessation of respiration is associated with two changes-loss of glycerol kinase activity and complete disappearance of pyridine nucleotides. Under other cultural conditions in which respiratory inhibition is less complete and more transitory, the losses of pyridine nucleotides are smaller and the rises which follow are correlated with increases in respiratory activity.