Tomiko Asakura

Neoculin as a New Taste-modifying Protein Occurring in the Fruit of Curculigo latifolia

A unique taste-modifying activity that converts the sense of sourness to the sense of sweetness occurs in the fruit of the plant Curculigo latifolia, intrinsic to West Malaysia. The active component, known as curculin, is a protein consisting of two identical subunits. We have found a new taste-modifying protein, named neoculin, of the same origin. Both chemical analysis and cDNA cloning characterized neoculin as a heterodimeric protein consisting of an acidic, glycosylated subunit of 113 amino acid residues and a basic subunit that is the monomeric curculin itself.

Characterization of the genes for two soybean aspartic proteinases and analysis of their different tissue-dependent expression

We isolated and characterized two cDNAs for aspartic proteinases (APs; EC 3.4.23) in soybean [Glycine max (L.) Merr.]. The encoded enzymes, soyAP1 and soyAP2, share 55% amino acid sequence identity. Northern analysis demonstrated that soyAP1 is expressed specifically in seeds, especially in dry seeds, while the expression of soyAP2 takes place in various tissues such as roots, stems, leaves and flowers, but not in dry seeds. SoyAP1 is highly expressed even at an early stage of germination, with a subsequent decrease in expression intensity. In contrast, the soyAP2 mRNA level increases 48xa0h after imbibition. To elucidate the physiological functions of soyAPs, we investigated the localization of soyAP expression in seeds germinating for 48xa0h at 25°C. SoyAP1 shows cell-type-specific expression in sieve tube cells of the hypocotyl. At the root tip, soyAP1 is expressed in immature tracheary elements and sieve tube cells, and its expression pattern changes with distance from the tip; strong signals observed throughout phloem converge gradually to sieve tube cells, whereas those observed in tracheary elements disappear while the elements are still immature. On the other hand, soyAP2 signals were detected broadly in the boundary region between the cortex and the central cylinder. These results suggest that soyAP1 and soyAP2 are functionally different from each other.

Time-course characteristics for the digestion of endogenous as well as exogenous protein in the small intestine: a case study with rats fed a [15N]-soy protein isolate.

A study was conducted to evaluate a net value of exogenous (dietary) protein nutrition in rats fed a [15N]-labeled soy protein isolate (SPI). Although [15N]-SPI-derived nitrogen reached a plateau 2 hr after feeding, it accounted for only a half of the total nitrogen in the small intestine. 15N was confirmed that was normally transported to liver, kidney, spleen, and brain. The present study reveals the large degree of participation of endogenous proteins in dietary SPI during small-intestinal digestion.