method of subjecting the same to point mutation such as converting at random using pcr or to site directed mutagenesis which is a known technology of site directed substitution or deletion mutation using commercially available kits a method of selectively cleaving this recombinant plasmid dna then removing or adding the selected oligonucleotide and linking the plasmid and an oligonucleotide mutagenesis method subsequently the recombinant dnas treated as above are purified using demineralized column such as qiagen funakoshi to obtain various recombinant dnas using various recombinant dnas thus obtained e coli k12 preferably e coli dh5 u03b1 e coli jm109 toyobo xl1 blue steatagene for example can be transformed or transduced to obtain transformants or transductants comprising recombinant dnas carrying sarcosine oxidase genes with various mutations introduced further for example in the case of transformants the following non limiting methods can be used to obtain strains producing sarcosine oxidases with the intended properties from the transformants obtained which contain recombinant plasmid dnas comprising various mutated sarcosine oxidase genes first said transformants obtained are transferred to ty agar mediums with respect to each colony and cultivated agents such as ampicillin may be added at this time as necessary after cultivation colonies are transferred to two ty agar mediums as above using transfer membrane cultivated for about 20 hours to produce sarcosine oxidases inducers such as iptg.