Inhibition of angiotensin I converting enzyme (ACE) by extracts prepared from immature and mature misos with deionized water was investigated. From the IC values of ACE obtained by using the extracts from mature misos, the inhibition of ACE was shown to be higher in the order of soybean-koji miso, rice-koji miso, and barley-koji miso. The inhibition was also different between immature and mature misos. The inhibition by the retentates of the extracts from soybeans and mature miso were decreased greatly by dialyzing the extracts against deionized water, while those of the dialyzates were still high and slightly increased as compared with the undialyzed extract. As the inhibitory components in the extract were considered to be such dialyzable substances as phytic acid, peptides, and browning substance, the inhibition of ACE by inositol phosphates was studied. The percentage inhibition of 2.5 mM phytic acid solution was 55.7%, but inositol and inositol tris- to penta-phosphates were scarcely inhibitory. Inositol mono- and bis- phosphates also showed weak inhibition. The organic phosphorus contents of the extracts form mature rice-koji miso, barley-koji miso, and soybean-koji miso were 36, 13, and 20 mg/100 mg, respectively. These results suggest that certain dialyzable substances having low molecular weight other than phytic acid participate in the inhibition of ACE.
