| Research Abstract |
An insoluble "high-molecular-weight fraction" centrifugally separable from Protin^R-digested soy protein isolate has been referred to as HMF, which has a high capacity to capture bile acids and to accerelate their fecal excretion. A significant correlation was observed for the fecal excretion of nitrogen, lipid and acidic or neutral steroid in HMF-fed rats. Therefor, the feces from HMF-fed rats were rinsed out in pH 7.4 phosphate buffer, 70% ethanol and 1% Triton-containing 8M urea, and the resulting insoluble residue was examined for its amino acid composition and bile acid-caturing capacity. The constituent amino acids were Leu > Ala > Val, Ile > Gly > Phe > Pro > Tyr > Ser > Glu etc. in order of molar ratio, being quite similar in pattern to those of the remnant after artificial digestion with mammalian digestive enzymes. The bile acid-capturing capacity turned out to be 14 μmol/g feces which was nearly compatible with the amount of bile acids extractable from powdered whole feces w
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ith 70% ethanol after washing with the phosphate buffer. Accordingly the HMF remnant as well as the insoluble feces should be called "soybean resistant protein" with due consideration for no more digestible characteristic. A comparison of bile acid-capturing capacity was made by equilibrium dialysis on litocholic acid (LCA), deoxycholic acid (DCA), chenodeoxycholic acid (CDCA), hyodeoxycholic acid (HDCA), taurodeoxycholic acid (TDCA), glycocheno-deoxycholic acid (GCDCA), ursodeoxycholic acid (UDCA) and cholic acid (CA). Consequently, soybean resistant protein had a high affinity for bile acids in order of LCA, DCA, CDCA >> HDCA > TDCA, GCDCA > UDCA, CA. Noteworthily there was a clear difference between DCA and CA in that respect. This difference was also ascertained from a pattern of uncompetitive inhibition by DCA in Eadie-Scatchard plot of bound CDCA against its corresponding bound/free ratio with the aid of ^<14>C-CDCA. When its bile acid-capturing capacity was compared with those of various resistant proteins prepared by artificial digestion from leguminous and cereal food proteins, any preparation was far inferior to soybean resistant protein in affinity for secondary bile acid. The majority of primary bile acids escaped from intestinal absorption undergo dehydroxylation by enteric bacteria and convert to secondary bile acids fairly risky as promorter for carcinogenesis. Taking into account such a high affinity of resistant proteins for secondary bile acids, their successive intake in ordinary eating habits contributes greatly to cancer prevention besides inprovement in lipidemia or cholesterolemia. Less
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