Activity and Stability of a New Sweet Protein with Taste-modifying Action, Curculin

Curculin elicited a sweet taste. After the sweetness of curculindiminished, application of deionized water or an acid to thetongue induced a sweet taste. The maximum sweetness of curculinitself was equivalent to thesweetness of 0.35 M sucrose. Themaximum sweetness induced by 0.02 M citric acid or deionizedwater after curculin dissolved in a buffer of pH 6.0 was heldin mouth for 3 min was also equivalent to that of 0.35 M sucrose.The sweetness induced by deionized water was completely suppressedby the presence of 1 mM CaCl₂ or MgCl₂, while that induced byan acid was not suppressed by the presence of divalent cations.Based on these results, the mechanism of the taste-modifyingactivity was discussed. Stability of curculin was examined undervarious conditions. The taste-modifying activity of curculinwas unchanged when curculin was incubated at 50°C for 1h between pH 3 and 11.     

A selection system for diploid and against haploid cells inSchizosaccharomyces pombe

We have isolated a mutant ofSchizosaccharomyces pombe whose growth is temperature sensitive when it is haploid but not when it is diploid. This mutant may provide a useful system for selecting nonconditional mutants which are defective in diploid formation upon conjugation.     

Chromogranin A (CGA) in the gastro-entero-pancreatic (GEP) endocrine system

Summary Chromogranin A (CGA), a protein at first detected in the adrenal medulla, has recently been found also in other organs, e.g. the endocrine pancreas. However, immunohistochemical findings concerning the cellular source of pancreatic CGA were controversial. Therefore, the endocrine pancreas of 10 mammalian species (man, tupaia, mole, cat, dog, pig, guinea pig, rabbit, rat) was investigated immunohistochemically for CGA-like immunoreactivities on serial semithin plastic sections using a high-titer polyclonal antiserum against bovine CGA. The results show that basically all pancreatic endocrine cell types are CGA-immunoreactive; however, every species has its own pattern of CGA-immunoreactive cell types. Other findings of the present studies indicate that the physiological function of CGA in pancreatic endocrine cells is related to the storage mechanisms of peptide hormones. Finally, a methodological approach is given to obtain not only qualitative but also semiquantitative data during immunohistochemical investigations.     

Targeting of Chrolamphenicol Acetyltransferase to Human Immunodeficiency Virus Particles via Vpr and Vpx

Vpr and Vpx are the auxiliary proteins of human immunodeficiency viruses (HIVs) selectively incorporated into mature viral particles. We showed that the bacterial chloramphenicol acetyltransferase (CAT) fused to the N-terminus of HIV-1 Vpr, HIV-2 Vpr, or HIV-2 Vpx was incorporated into mature virions in a type-selective manner. By using chimeric proteins between HIV-1 Vpr and HIV-2 Vpx, we found that the N-terminal side of these proteins was mainly important for type-selective virion incorporation. The C-terminal arginine-rich region of HIV-1 Vpr was also found to transport CAT fusion proteins into virions but without any type selectivity. Furthermore, the corresponding regions of HIV-2 Vpr and HIV-2 Vpx had no such activity. This region of HIV-1 Vpr may interact nonspecifically with viral genomic RNA. Collectively, Vpr and Vpx may provide a means to introduce foreign proteins and other molecules into HIV virions for therapeutic purposes.     

Degradation of dehydroascorbate to 2,3-diketogulonate in blood circulation

In our previous paper (Biochim. Biophys. Acta 1379 (1998) 257–263), we demonstrated that bicarbonate promotes a cleavage of lactone ring of dehydroascorbate (DHA) on the basis of in vitro experiments. In the present study, we examined the degradation of DHA in blood circulation in vivo by using a high-performance liquid chromatographic method for the determination of ascorbate (AsA), DHA and 2,3-diketogulonate (2,3-DKG), which required no pretreatment of biological fluids. When DHA was intravenously administered to rats, a rapid disappearance of DHA (t_1/2<1 min) and a concomitant appearance of 2,3-DKG in blood circulation were observed. Approximately 90% of the administered DHA were excreted into urine as resulting 2,3-DKG (55%) and AsA (31%), respectively. Furthermore, we elucidated that rat plasma lacks an enzyme having an aldonolactonase-like activity. The result of the present study suggests that this DHA disappearance is a function of both a chemical degradation to 2,3-DKG and a reduction to AsA.     

The Effects of lithium and Zinc Ions on the Pattern of Acidic Glycans in the Sea Urchin (Hemicentrotus pulcherrimus) Embryo

Among several acidic glycan components found in Hemicentrotus embryos, the "F"- and "S"-components were specifically affected by treatment with Li⁺and Zn²⁺, respectively. The amount of the "F"-component in Li⁺-treated embryos was about 60% that in normal embryos. This fact was in accordance with the reduced alcian blue staining of the surfaces in Li⁺-treated embryos. Moreover, the "F"-component in Li⁺-treated embryos appeared to be composed of two subcomponents, while in normal and Zn²⁺-treated embryos it appeared to be single. The "S"-component in Zn²⁺-treated embryos was about 8% that in normal embryos. According to histochemistry with a lectin probe, it was found that UEA-I was much more strongly associated with a hyaline layer in Li⁺-treated than in normal and Zn²⁺-treated embryos. Li⁺-treated embryos developed into exogastrulas, which were divided by a constriction into two parts; an animal half which stained intensely with alcian blue, and a vegetal half which stained poorly. On the other hand, Zn²⁺-treated embryos remained as permanent blastulas. Considering the above, it is suggested that change in the acidic glycan pattern leads to alterations in the morphogenesis of sea urchin embryos.