Exposure Of New Sites Research Articles

중력 장-흐름 분획법을 이용한 전분 입자의 swelling에 관한 연구

물의 흡수에 의한 전분알갱이의 swelling은 물과 친화력이 있는 새로운 부분의 노출에 의하여 구조적인 변화로써 점진적으로, 때로는 갑작스럽게 변화를 일으킨다. 이러한 이유로 인해서, 물과의 접촉 시간에 따르는 전분 알갱이의 크기 또는 모양의 변화에 관심을 가진다. 중력 장-흐름 분획법(gravitation field-flow fractionation, GrFFF)은 마이크론 범위의 크기를 가지는 입자들을 분리하는 데에 유용한 분리기술이다. 본 연구에서는 감자와 고구마 전분알갱이들의 크기와 크기 분포도를 결정하는 데에 있어서 GrFFF의 응용가능성을 검사하고자 한다. GrFFF를 이용하여 물과의 접촉 시간에 따르는 전분 알갱이들의 크기분포도 변화를 모니터하였다. GrFFF로부터 얻어진 전분알갱이들의 크기 및 크기분포는 광학현미경(optical microscopy, OM) 결과와 비교하였다. 결과적으로 감자와 고구마 전분의 swelling은 물과의 접촉시간이 증가함에 따라 전분알갱이의 크기가 증가하며, 전분의 종류가 달라지면 swelling 속도가 달라짐을 확인하였다. Swelling of starch granules by water-sorption causes a progressive or sometimes abrupt change in sorption behavior as a result of structural alterations and the possible exposure of new sites with high affinity for water. It is thus of interest to examine the time-dependent change in the size or shape of the starch granules. Gravitational field-flow fractionation (GrFFF) utilizes the earth's gravity as the external field, and is useful for separation of micron-sized particles with larger particles eluting earlier than smaller ones. In this study, GrFFF was used to monitor the swelling of two starch granules, potato starch and sweet potato starch during contact time of 11-12 days at room temperature in water. Results from GrFFF were compared with those obtained from optical microscope (OM). For both starch granules, the mean sizes were increased with time spent in water.

Cooperative multiple binding of BisANS and daunomycin to tubulin

The binding of daunomycin and bisANS to tubulin was studied by direct equilibrium techniques. Both ligands generated abnormal Scatchard plots. Their concave-downward nature indicated positive cooperativity. The data conform to tubulin possessing ca. 35 daunomycin binding sites with a binding constant of 570-1430 M-1. The binding of bisANS is characterized by 1 strong binding site (KA = 4.5 x 10(5) M-1) and 40-50 lower affinity sites. Hill plots of both showed low degrees of cooperativity (m = 1.8 for daunomycin and 2.3 for bisANS). A detailed analysis was carried out of the cooperativity of binding of daunomycin to tubulin. Concentration differences spectra and sedimentation velocity analysis of daunomycin showed that this molecule undergoes self-association in the drug concentration range used in the binding study. The low level of polymerization (approximately tetramer), however, indicated that this could not be the source of the observed cooperativity between 35 molecules. Both the shape and concentration dependence of the daunomycin concentration difference spectra were strikingly similar to those generated on the binding of daunomycin to tubulin, which indicates the stacking of daunomycin in both cases. The observed Scatchard plot of the binding was found to be consistent with a process that involves in part ligand-ligand interactions when complexed to tubulin. Examination of the binding of bisANS in the presence of daunomycin revealed a strong increase of bisANS binding to tubulin, which suggests a loosening of tubulin structure with the exposure of new sites as these ligands bind. The mutual interaction between the two ligands in dilute solution was demonstrated by difference spectroscopy.(ABSTRACT TRUNCATED AT 250 WORDS)

Alterations in pyridoxal 5'-phosphate inhibition of human erythrocyte anion transport associated with osmotic hemolysis and resealing.

When pyridoxal 5'-phosphate (PLP) is covalently bound to band 3 protein in intact red blood cells and those cells are subjected to the osmotic hemolysis and resealing process, a significant reduction in the original PLP anion transport inhibitory potency occurs. We show that partial deinhibition is not due to the development of a second anion transport pathway in resealed ghosts. Rather, partial deinhibition arises from a hemolysis-induced conformational change in CH17 (17-kDa integral chymotryptic domain of band 3). This change causes the extracellular exposure of new transport inhibitory sites. Exposure of the new sites leads to a 2-fold increase in PLP labeling of CH17 in resealed ghosts compared with CH17 in intact red cells. The hemolysis and resealing process has no effect on the labeling of CH35 (35-kDa integral chymotryptic fragment of band 3). Double-labeling studies show restoration of transport inhibitory potency to near red cell levels when the newly exposed CH17 sites are labeled with PLP in resealed ghosts. The results support the view that CH17 contains PLP transport inhibitory sites. They show that a major conformational change occurs in band 3 with hemolysis.

Primary structure of human erythrocyte glycophorin A. Isolation and characterization of peptides and complete amino acid sequence.

Peptides of glycophorin AMN were prepared by cyanogen bromide cleavage and by chymotryptic and tryptic digestion. Cyanogen bromide cleavage produces three fragments which account for the entire polypeptide chain. Trypsin and chymotrypsin cleave completely at several sites, but incompletely at sites within the glycosylated segment of the polypeptide chain. Some of the latter sites become accessible to proteolysis after desialation in addition to exposure of new sites for cleavage. The amino acid sequence of glycophorin AMN has been determined by manual Edman degradation, using both the direct Edman and the dansyl-Edman procedures simultaneously for determination of glycosylated amino acid residues. The automated procedure was used for sequence determination of a hydrophobic peptide. Glycophorin A is a polypeptide chain of 131 amino acid residues and contains 16 oligosaccharide units attached to the amino-terminal third of the molecule. Fifteen oligosaccharides are linked O-glycosidically to either threonine or serine residues and one complex oligosaccharide unit is attached N-glycosidically to an asparagine residue. Amino-terminal sequences are different for glycophorin AM and AN, the two forms of the glycophorin A molecule coded for by genes at the MN locus. The differences in sensitivity to proteases of various sites on glycophorin A seem to be due to heterogeneity in the carbohydrate components and not to differences in the primary structure of the polypeptide chains. This work contains a number of revisions and corrections of earlier preliminary reports [Segrest, J.P., Jackson, R. chem. Biophys. Res. Commun, 49, 964-969; Tomita, M., & Marchesi, V.T. (1975) Proc. Natl. Acad. Sci. U.S.A. 72, 2964-2968].

Potentiation of phytomitogens action by neuraminidase and basic polypeptides.

TREATMENT of lymphocytes with neuraminidase enhances their blastogenic response to some antigens and mitogens1, increases their lectin-induced agglutinability2,3, antigenicity and immunogenicity4,5, alters their homing properties6 and renders the cells highly susceptible to the cytolytic effects of alloantibody and complement7,8. These changes might result from the exposure of new sites on the cell surface2,3,9, a reduction in the net surface charge of the cells or a combination of the two effects. Polycations agglutinate different cell types10–12 and markedly reduce their anodic electrophoretic mobility10. In order to study the effect of cell surface charge on lymphocyte blastogenic response to phytomitogens the effect of polycations on this process was compared with that of neuraminidase.