Soluble guanylate cyclase(sGC) is a critical heme-containing enzyme involved in NO signaling.The dimerization of sGC subunits is necessary for its bioactivity and its mechanism is a striking and an indistinct issue.The roles of heme domain cysteines of the sGC on the dimerization and heme binding were investigated herein.The site-directed mutations of three conserved cysteines(C78A,C122A and C174S) were studied systematically and the three mutants were characterized by gel filtration analysis,UV-vis spectroscopy and heme transfer examination.Cys78 was involved in heme binding but not referred to the dimerization,while Cys174 was demonstrated to be involved in the homodimerization.These results provide new insights into the cysteine-related dimerization regulation of sGC. Soluble guanylate cyclase (sGC) is a critical heme-containing enzyme involved in NO signaling. The dimerization of sGC subunits is necessary for its bioactivity and its mechanism is a striking and an indistinct issue. The roles of heme domain cysteines of the SGC on the dimerization and heme binding were carried herein. The site-directed mutations of three conserved cysteines (C78A, C122A and C174S) were studied systematically and the three mutants were characterized by gel filtration analysis, UV-vis spectroscopy and heme transfer examination. in heme binding but not referred to the dimerization, while Cys 174 was demonstrated to be involved in the homodimerization. These results provide new insights into the cysteine-related dimerization regulation of sGC.