The sedimentation characteristics of deoxyribonucleic acid from human tissues.

1. Evidence is presented for the presence of pyridoxamine phosphate oxidase and a pyridoxal phosphate phosphatase in aqueous extracts of E8cherichia coli. 2. Spectrophotometric methods have been developed for the precise measurement of substrate and product concentrations in both enzyme systems. Specific activities of the order of 10-2 tumole/30 min./mg. ofprotein/ml. ofreaction mixture are reported. 3. Pyridoxamine phosphate oxidase was inhibited by dialysis, and further inhibition was caused by pyruvate, ao-oxoglutarate and oxaloacetate at a concentration of 0-02 mm. Inhibition of activity by mepacrine suggests that a flavin coenzyme is involved. 4. Pyridoxal phosphate phosphatase was also found to be highly active in mammalian 'alkaline'phosphatase preparations. The E8cherichia coli extracts used exhibited high 'acid '-phosphatase and low 'alkaline '-phosphatase activities when disodium phenyl phosphate was used as substrate. No dephosphorylation of pyridoxamine phosphate could be detected. 5. The presence of glucose in Escherichia coli growth medium increased the relative amount of phosphatase compared with oxidase activity.