Isomaltooligosaccharides (IMO) are a mixture of isomaltose, isomaltotriose, panose, isomaltotetraose, etc. IMO and its hydrogenated derivative (IMH) were characterized for their luminal clearance from rat jujunum loops as the indication of their digestibility. They were compared with a disaccharide fraction (IM2) and a higher oligosaccharide fraction (IM3) prepared from IMO, typical digestible saccharides (maltose, maltotriose, and sucrose), and typical nondigestible saccharides (maltitol, raffinose, and fructooligosaccharides (FO)). The clearance rate of IMO was significantly smaller than that of IM2, which was mainly composed of isomaltose (64.3%), and digestible saccharides, and significantly larger than that of nondigestible saccharides. That of IM2 was almost the same as that of sucrose or maltotriose but significantly smaller than that of maltose. That of IM3 tended to be smaller than that of IMO, and larger than that of nondigestible saccharides. That of IMH was significantly smaller than that of IMO and similar to that of maltitol. These results seem to indicate that IMO is slowly digested in the jejunum, that the components having higher degree of polymerization of IMO are less digestible, and that IMH is nondigestible.

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An extracellular protease derived from the culture broth of a microorganism, a Streptomyces species, produced Boc-Pro-Pro and diproline from Boc-Pro-Pro-Pro-Pro. The enzyme was purified 726-fold, with a yield of 2.6%, by ammonium sulfate fractionation, ion-exchange chromatography, and gel filtration chromatography. The molecular weight of the enzyme was determined to be 65,000 by gel filtration and 70,000 by SDS-PAGE. The enzyme released a C-terminal dipeptide from peptide substrates having a C-terminal proline and a penultimate proline or alanine residue, but did not hydrolyze angiotensin I or bradykinin. When the enzyme hydrolyzed Leu-Pro-Pro-Pro-Pro-Pro, it produced Leu-Pro-Pro-Pro and Pro-Pro before producing Leu-Pro. The enzyme thus seems to be a kind of dipeptidyl carboxypeptidase, its substrate specificity being very different from that of the well known dipeptidyl carboxypeptidases [EC 3.4.15.1] such as the angiotensin-converting enzyme.

No abstract