This study was purposed to design the economical and easily recognizable sensing system for the detection of methyl mercaptan(MM) at ppb level which was a representative of halitosis. Methyl mercaptan oxidase(MMO) was selected as a molecular receptor of the biosensor.
MMO was isolated from T. thiooxidans, T. thioparus, and R. rhodochrous. The procedure of purification involved DEAE-Sephacel and Superose 12 column chromatography and the maximum recovery yield was obtained from R. rhodochrous. Each strain had a unique characteristic about salt effect. Concerning the effect of organic solvents, 10% methanol did not affect the activity of MMO from T. thioparus at all and MMO from T. thiooxidans remained the good activity against the addition of 20% ethanol. The optimum temperatures for enzyme activity were 43, 55, and 60℃ to each strain. The molecular weights of MMO had similar values from 64 to 68 kDa by the analysis using SDS-PAGE. Methyl yellow method showed a recognizable color change by addition of formaldehyde over 450 nmol. Purpald and TMB method had good sensitivities over tens nmol of formaldehyde and hydrogen peroxide.
