Involved in the toluene-4-sulfonate degradation pathway. Monomer. Part of the p-toluenesulfonate methyl-monooxygenase complex TsaBM, comprising the reductase TsaB and the oxygenase TsaM. Could be the product of a pseudogene. Probably not expressed, due to the absence of promoter-like sequences upstream of the operon tsaMBCD2 (PubMed:11282598).