A continuous fluorometric assay for flavokinase. Properties of flavokinase from Peptostreptococcus elsdenii.

A continuous fluorometric assay that utilizes apoflavodoxin as a trapping agent for riboflavin 5'-phosphate (FMN) has been developed for flavokinase (ATP:riboflavin 5'-phosphotransferase, EC 2.7.1.26). Use of this assay is illustrated in a procedure for the partial purification of flavokinase from the strict anaerobe Peptostreptococcus elsdenii. The purified enzyme catalyzed the formation of 8.3 nmol FMN - min-1 - mg-1 at 37 degrees C and had apparent Km values for riboflavin and ATP of 10 and 4.7 micronM, respectively. ATP could be replaced by ADP (22% of the rate observed with ATP) but not by GTP. The enzyme also phosphorylated 5-deaza- and 8-bromoriboflavin with activities of 15 and 70%, respectively, of that with riboflavin; it was inactive with iso riboflavin and deoxyriboflavin.