常山凝集素的分离纯化及其性质研究

 本文采用分子筛层析和离子交换技术,从植物常山(Dichroa febrifuga Lour)的鲜叶中,分离纯化出一种新的凝集素,定名为常山凝集素(DFL)。并对其理化性质进行了鉴定:测得其亚基分子量为37,000道尔顿;等电点为4.2。DFL是一种糖蛋白,糖含量为2.8％。DNS-CI法测得其肽链的N-末端为L-缬氨酸。本文还对其糖专一性、不同动物红细胞的凝集专一性,以及对猪精子和某些肿瘤细胞的凝集活性等生物学性质进行了研究。     

Structural and evolutionary consequences of unpaired cysteines in trypsinogen

Vertebrate trypsins usually contain six disulfide bonds but human trypsin 1 (PRSS1) contains only five and human trypsin 2 (PRSS2) contains only four. To elucidate possible evolutionary pathways leading to the loss of disulfide bonds, we have constructed mutants lacking one or two cysteines of four disulfide bonds (C22-C157, C127-C232, C136-C201, and C191-C220) in rat anionic trypsinogen and followed their expression in the periplasm of Escherichia coli. When both cysteines of any of the above-mentioned disulfide bonds were replaced by alanines we found, as expected, proteolytically active enzymes. In the case of C127-C232 (missing from both human trypsins) and C191-C220 both single mutants gave active enzymes although their yield was significantly reduced. In contrast, only one of the single mutants of disulfide bonds C22-C157 and C136-C201 (missing from human trypsin 2) was expressed in E. coli. In the case of these disulfide bonds, we obtained no expression when the solvent accessible molecular surface of the free cysteine residue was the smaller one, indicating that a buried unpaired cysteine was more deleterious than one on the surface of the molecule.     

Genetic variation in a geographically restricted and two widespread species of South American Nothofagus

The amount and distribution of genetic variation is compared using starch gel electrophoresis among populations of the three evergreen species of South American Nothofagus : the geographically restricted Nothofagus nitida (Phil.) Krasser and the widespread Nothofagus betuloides (Mirb.) Oerst. and Nothofagus dombeyi (Mirb.) Oerst. Ten enzyme systems were resolved coding for fifteen putative genetic loci. N. betuloides and N. dombeyi were more genetically variable than N. nitida ; they had higher total number of alleles, mean number of alleles per locus, percent of polymorphic loci, mean expected heterozygosity, and mean total genetic diversity. These results are in agreement with the hypothesis that widespread species are often associated with historically large and more continuously distributed populations which in turn can maintain higher levels of genetic variation. Conversely, the genetic structure of N. nitida including its low genetic identity with the other two species and the presence of four unique alleles support the hypothesis that N. nitida has been isolated from the other two species for a considerable period of time. Genetic data in concert with the fossil record indicate that these taxa may be members of a pre-Pleistocene flora and consequently their genetic structures reflect a more ancient evolutionary history than previously hypothesized.