Interspecific agonistic behaviour in small mammals in a Mexican high-elevational grassland

Field trials were conducted throughout an annual cycle to study the role of agonistic behaviour in explaining the relative abundance of the volcano mouse ( Neotomodon alstoni ) in a small mammal community in high-altitude grasslands of central Mexico. Intrasexual contests between N. alstoni and three other sympatric rodents ( Peromyscus melanotis, Microtus mexicanus, and Reithrodontomys megalotis ) were performed. Male and female P. melanotis (100 and 67% of contests, respectively) and M. mexicanus (82 and 100%) were aggressively dominant over N. alstoni , whereas R. megalotis (80 and 100%) were not aggressive. Agonistic behaviour in this species did not explain its greater abundance in the community.     

Base sequence damage in DNA from X-irradiated monkey CV-1 cells

Two kinds of 3'-ends were detected in DNA scission fragments of highly repetitive primate component alpha DNA which were isolated from irradiated monkey CV-1 cells. The fragments' 3'-ends were characterized by 5'-32P-end labelling the DNA, followed by examination in high-resolution polyacrylamide gels under denaturing conditions. Hydrolysis of the labelled fragments' termini with exonuclease III of E. coli or by the 3'-phosphatase activity of T4 polynucleotide kinase generated a third, slowest migrating species in each mobility size class. Reference to mobility size class standards makes it highly probable that the fragment ends generated by X-rays in cells are 3'-phosphoryl and 3'-phosphoglycolate, and that they are converted to slower migrating fragments with 3'-OH ends, similar to results obtained with DNA irradiated in water (Henner et al. 1982, 1983 a, b). Densitometer measurements of gel autoradiograms showed that X-ray induction of DNA fragments with 3'-phosphoryl and 3'-phosphoglycolate ends was dose-dependent over a range 100-900 Gy. In CV-1 cells the frequency of single-strand breaks in alpha DNA was 8.6 x 10(-7) breaks/nt/Gy. The two kinds of ends disappeared in post-radiation incubation with a half-time of 1.6 h. These results provide a new means to study X-ray damage and repair of specific sequences in animal cells.     

Clinical Use of a New Mitral Disc Valve

A disc valve of new design was used successfully for the replacement of the mitral valve in patients with rheumatic mitral valve disease. This valve would appear to have the following advantages over the mitral ball valve prosthesis:• Lower left atrial pressure after replacement.• Elimination of the hazard of left ventricular outflow tract obstruction with mitral valve replacement.• Decreased incidence of thromboembolization.• Abolition of possibility of ventricular septal irritation.Despite the better outlook for this valve compared with the ball valve for mitral valve substitution, the mitral valve should always be repaired whenever feasible. Repair is possible in the majority of patients.     

蚕豆叶片发育与衰老过程中超氧物歧化酶活性与丙二醛含量变化

蚕豆植株叶片随茎节自上而下表现出明显的发育与衰老顺序,可作为衰老特征的是叶绿素和蛋白质含量明显下降。蚕豆叶中SOD活性主要定位于12 000× g离心后所得的上清液和叶绿体组分。衰老叶片的SOD总活性和叶绿体组分的相对活性都有所下降,SOD同工酶谱也发生了改变。O_2~ 产生速率随叶龄增大而稍上升;而MDA含量在叶片外观表现枯黄衰老征兆前就急剧上升。可能因为衰老叶片过氧化氢酶活性大幅度下降与SOD之间的不平衡,致使O_2~ 代谢中间产物累积而引起膜的损伤.     

Cellular localization and characterization of proteins that bind high density lipoprotein.

High density lipoprotein (HDL) stimulates excretion of excess intracellular cholesterol from cells, presumably by interacting with a cell-surface receptor. A 110 kDa membrane protein that is a candidate for the HDL receptor has been identified by ligand blot analysis. In this study we determined the cellular localization of this and other HDL-binding proteins and characterized their properties. The plasma membranes (PM) of cultured bovine aortic endothelial cells were labeled with trace amounts of [3H]cholesterol, and cell homogenates were fractionated on sucrose and Percoll gradients. Ligand blot analysis of homogenates of cultured bovine aortic endothelial cells demonstrated that cells contain multiple proteins that bind HDL3, including a major membrane protein with an apparent M(r) of 110 kDa and two minor ones with M(r) of 105 and 130 kDa. The gradient distribution of the 105, 110, and 130 kDa HDL-binding proteins mirrored that of labeled cholesterol and 5'-nucleotidase, both PM markers. Treatment of intact cells with the water-soluble cross-linker bis(sulfosuccinimidyl)suberate abolished the HDL binding activity of the 110 and 130 kDa proteins but not that of the 105 kDa protein. These findings suggest that the 105, 110, and 130 kDa HDL-binding proteins are localized to the PM and that at least two of these proteins are exposed to the extracellular fluid. Solubilized 110 and 130 kDa proteins were retained on wheat-germ agglutinin and abrin lectin columns, showing that they are glycoproteins. The cellular localization and physical properties of the 110 and 130 kDa proteins suggest that they may play a role in binding of HDL to the cell surface.     

Analysis of the activation process of porcine procarboxypeptidase B and determination of the sequence of its activation segment

The molecular events which lead to the proteolytic transformation of porcine procarboxypeptidase B (PCPB) in carboxypeptidase B (CPB) have been determined. Among pancreatic and other tested proteinases, trypsin is the only one capable of generating carboxypeptidase B activity from the zymogen, in vitro. In the first step of this process, trypsin produces cleavage at the boundary between the activation region and the CPB region. Subsequently, a definite sequence of cleavages occurs at the C-terminal end of the released activation segment of 95 residues, giving rise to characteristic intermediates and to a proteolytically resistant activation fragment of 81 residues. In this process, the newly formed CPB participates in the quick-trimming of the released activation peptides. Only a single CPB species is formed in the activation process. This fact and the inability of the released activation peptides to inhibit CPB--and, therefore, their inability to slow down the kinetics of appearance of CPB activity--are two important characteristics differentiating between the activation processes of procarboxypeptidases A and B. The sequence of the 95 residues (MW = 12,835) of the activation region of porcine PCPB has also been deduced, largely from the information obtained by Edman degradation of its fragments and in part by considerations of homology with the rat precursor. The porcine PCPB activation region contains a high percentage of acidic residues, lacks cysteines, methionines, and side-chain posttranslational modifications, and presents a low but significant homology (31%) with the corresponding sequence of porcine procarboxypeptidase A.     

Rapid screening of a YAC library by pulsed-field gel Southern blot analysis of pooled YAC clones

A new method for screening of YAC libraries is described. Individual YACs were pooled into groups of 384 clones and prepared as samples suitable for pulsed-field gel electrophoresis. A five hit human YAC library (Brownstein et al., 1989) containing approximately 60,000 clones was condensed into 150 such pools and chromosomal DNAs in each sample were separated on three pulsed field gels containing 50 samples each. Southern blots prepared from these gels were hybridized with probes of interest to identify pools containing homologous YACs. Further purification was performed using standard colony hybridization procedures. Twenty-one probes used thus far have identified 47 positive pools and corresponding YACs have been purified from 28 of these. Some significant advantages of this method include avoidance of DNA sequence analysis and primer generation prior to YAC screening and the ability to handle the entire library on three filters. The screening approach described here permits rapid isolation of YACs corresponding to unsequenced loci and will accelerate establishment of YAC contigs for large chromosomal segments.     

Biosynthesis of lysosomal hydrolases: their synthesis in bound polysomes and the role of co- and post-translational processing in determining their subcellular distribution

By in vitro translation of mRNA’s isolated from free and membrane-bound polysomes, direct evidence was obtained for the synthesis of two lysosomal hydrolases, β-glucuronidase of the rat preputial gland and cathespin D of mouse spleen, on polysomes bound to rough endoplasmic reticulum (ER) membranes. When the mRNA’s for these two proteins were translated in the presence of microsomal membranes, the in vitro synthesized polypeptides were cotranslationally glycosylated and transferred into the microsomal lumen. Polypeptides synthesized in the absence of microsomal membranes were approximately 2,000 daltons larger than the respective unglycosylated microsomal polypeptides found after short times of labeling in cultured rat liver cells treated with tunicamycin. This strongly suggests that nascent chains of the lysosomal enzymes bear transient amino terminal signals which determine synthesis on bound polysomes and are removed during the cotranslational insertion of the polypeptides into the ER membranes. In the line of cultured rat liver cells used for this work, newly synthesized lysosomal hydrolases showed a dual destination; approximately 60 percent of the microsomal polypeptides detected after short times of labeling were subsequently processed proteolytically to lower molecular weight forms characteristic of the mature enzymes. The remainder was secreted from the cells without further proteolytic processing. As previously observed by other investigations in cultured fibroblasts (A. Gonzalez-Noriega, J.H. Grubbs, V. Talkad, and W.S. Sly, 1980, J Cell Biol. 85: 839-852; A. Hasilik and E.F. Neufeld, 1980, J. Biol. Chem., 255:4937-4945.) the lysosomotropic amine chloroquine prevented the proteolytic maturation of newly synthesized hydrolases and enhanced their section. In addition, unglycosylated hydrolases synthesized in cells treated with tunicamycin were exclusively exported from the cells without undergoing proteolytic processing. These results support the notions that modified sugar residues serve as sorting out signals which address the hydrolases to their lysosomal destination and that final proteolytic cleavage of hydrolase precursors take place within lysosome itself. Structural differences in the carbohydrate chains of intracellular and secreted precursors of cathespin D were detected from their differential sensitivity to digestion with endoglycosidases H and D. These observations suggest that the hydrolases exported into the medium follow the normal secretory route and that some of their oligosaccharides are subject to modifications known to affect many secretory glycoproteins during their passage through the Golgi apparatus.