Altered diaphorase activity in optochin-resistant pneumococci.

Methylene blue (MB) reductase activities of washed cell suspensions and of cell-free extracts prepared from optochin-resistant mutant pneumococci were two times greater than and four to eight times more resistant to optochin inhibition than those of similar preparations from the optochin-sensitive parent strains. With whole cells, optochin hydrochloride was approximately four times more potent than quinine hydrochloride in inhibiting MB reductase activity. However, with cell-free extracts, both drugs had similar inhibitory activities. Glucose uptake was not affected by optochin hydrochloride, and both optochin-sensitive and optochin-resistant pneumococci had similar glucose uptake patterns. Diaphorase activities of cell-free extracts prepared from optochin-resistant pneumococci were two times greater than and four to eight times more resistant to optochin inhibition than those of cell-free extracts prepared from the optochin-sensitive parent strains. Flavin concentrations of cell-free extracts prepared from optochin-sensitive and optochin-resistant strains were similar.