An expression system of recombinant myoglobins (Mb) of 3 scombridae fish species was constructed. The stability of these Mbs was compared with native Mbs purified from slow skeletal muscle. The addition of hemin during the cultivation of an Escherichia coli strain harboring a pGEX-2T expression vector was found to be necessary to prevent recombinant Mb from degrading and to attain its proper folding. The stabilities of recombinant Mbs were generally lower than those of native Mbs, partly due to the absence of post-translational modification. The alpha-Helical content of bullet tuna recombinant Mb at 10 degrees C was the lowest (29.0%) among the recombinant Mbs examined (the values for bluefin tuna and bigeye tuna Mbs being 34.8 and 35.5%, respectively). On the other hand, the stabilities of recombinant Mbs of bluefin tuna and bigeye tuna against denaturants (urea and guanidine hydrochloride) were found to be similar, whereas bullet tuna recombinant Mb exhibited the lowest stability among these Mbs. The pattern of temperature-dependent decrease in the alpha-helical content supported these results.