The phylogeny of the hominoid primates: a statistical analysis of the DNA-DNA hybridization data

Sibley and Ahlquist compared the single-copy nuclear DNA sequences of the hominoid primates using DNA-DNA hybridization. From this data set they estimated a phylogeny that clusters man and chimpanzees using a distance Wagner procedure. However, no assessment of statistical confidence in this estimated phylogeny was made, despite the fact that their data set contains internal inconsistencies concerning the correct branching order. This paper presents a modification of Pielou's Q- statistic that allows one to make nonparametric tests of phylogenetic relationship from distance data. The results of this analysis indicate that the estimated phylogeny of Sibley and Ahlquist is without statistical significance owing to the internal inconsistencies of the data set. A survey and additional analyses of other types of molecular data indicate that the phylogeny that clusters chimpanzees and gorillas and has the human lineage splitting off earlier is statistically consistent with all the molecular data (including the DNA-DNA hybridization data), whereas the phylogeny estimated by Sibley and Ahlquist can be rejected at the 5% level using the data on restriction- endonuclease sites in the mitochondrial genome.      

Nitrate reductase: an improved assay method for phytoplankton

A new assay for measuring the activity of nitrate reductasein phytoplankton, based upon the permeability of cells treatedwith toluene to substrates and products, is described. The methodis simple and, since the reaction is carried out directly ona glass fiber filter, can be easily performed in the field oron shipboard. In comparison with previous methods, this techniquegave higher absolute amounts of NO^–₂ formed per unit tuneand higher enzymatic activities per sample volume when testedwith axenic algal cultures and with natural phytoplankton populationsfrom Lake Kinneret, the River Jordan and the Eastern Mediterranean.     

Interactions ofCandida albicans with bacteria and salivary molecules in oral biofilms

The yeastCandida albicans coaggregates with a variety of streptococcal species, an interaction that may promote oral colonization by yeast cells.C. albicans andCandida tropicalis are the yeasts most frequently isolated from the human oral cavity and our data demonstrate that both these species bind toStreptococcus gordonii NCTC 7869 while two otherCandida species (Candida krusei andCandida kefyr) do not. Adherence ofC. albicans was greatest when the yeast had been grown at 30° C to mid-exponential growth phase. For 21 strains ofC. albicans there was a positive correlation between the ability to adhere toS. gordonii and adherence to experimental salivary pellicle. Whole saliva either stimulated or slightly inhibited adherence ofC. albicans toS. gordonii depending on the streptococcal growth conditions. The results suggest that the major salivary adhesins and coaggregation adhesins ofC. albicans are co-expressed.     

Blown away? Wind speed and foraging success in an acoustic predator

Mammal Research - Foraging animals must contend with fluctuating environmental variables that affect foraging success, including conditions like wind noise, which could diminish the usefulness of...     

Assignment of the dipeptidylpeptidase IV (DPP4) gene to pig Chromosome 15q21

A porcine 2-kb partial dipeptidylpeptidase IV (DPP4, EC 3.4.14.5) cDNA clone and a porcine 16-kb genomic fragment containing parts of the DPP4 gene were isolated, characterized, and used as probes to map the DPP4 gene to pig Chr (Chr) 15q21 by fluorescence in situ hybridization. A two-allele RFLP was revealed for the DPP4 gene. This polymorphism was utilized in a linkage test against the erythrocyte antigen G (EAG), previously assigned to Chr 15, and the microsatellite S0088, which is linked to EAG. The linkage analyses revealed significant evidence for linkage confirming the assignment of DPP4 to Chr 15.     

Size and shape of two intestinal dipeptidases

Physicochemical parameters were determined on glycyl-L-leucine hydrolase (glycy-leucine dipeptidase, EC 3.4.13.2) and aminoacyl-L-proline hydrolase (proline dipeptidase, EC 3.4.13.9), purified from pig small intestine. The native molecular weights were found to be 115,000 and 113,000, respectively, as determined by a sedimentation equilibrium technique. Under denaturing conditions the molecular weights were found to be 51,000 and 63,200, respectively, using the same technique. It is concluded that each dipeptidase is composed of two subunits of equal molecular weight. The two dipeptidases have the same Stokes radius, 4.2 nm, analysed by gel chromatography. The sedimentation coefficients were found to be 5.8. S and 6.5 S and the intrinsic viscosities 5.4 ml/g and 5.8 ml/g, respectively. For both dipeptidases the measured physicochemical parameters are in accordance with the model of a prolate ellipsoid of revolution, having an axial ratio of about 5.     

Changes of the quaternary structure of microvillus aminopeptidase in the membrane

Microvillus aminopeptidase (EC 3.4.11.2) is an enzyme with a molecular weight around 300 000. Normal preparations contain three different subunits (subunit A, Mr 162 000; subunit B, Mr 123 000; subunit C, Mr 61 000). The relationship between the three subunits was studied by immunoelectrophoresis using specific antibodies against individual denatured subunits and by densitometric scanning of polyacrylamide gels after separation of the three subunits. The results suggest that microvillus aminopeptidase initially appears in the membrane as a symmetric molecule built up to two identical A subunits. These subunits are then split into equimolar amounts of subunit B and subunit C by trypsin. Subunit B cannot generate subunit C but may be further degraded. The reaction sequence described is one which occurs in vivo. Treatment of purified aminopeptidase with trypsin increases the specific activity twofold. This phenomenon does not seem to be correlated to the generation of subunit B and subunit C or to the transformation of amphiphilic form into hydrophilic form.     

Evidence for an apical sorting signal on the ectodomain of human aminopeptidase N.

In polarized epithelial cells aminopeptidase N is targeted to the apical membrane. The aim of this study was to determine whether a sorting signal is necessary for its correct transport to the apical membrane and, if so, to localize this sorting signal to one of the domains of the transmembrane protein. Anchor-minus aminopeptidase N, consisting of the hemagglutinin signal peptide including its cleavage site, and the ectoplasmic domain of human aminopeptidase N were stably expressed in Madin-Darby canine kidney cells cultured on polycarbonate filters. By measurement of the enzymatic activity it was found that the anchor-minus aminopeptidase N was secreted in a polarized manner to the apical side. As a reference the secretion of the secretory granule protein, cystatin C, was likewise studied. Cystatin C was found to be secreted in a nonpolarized manner to both domains. Our data thus show that human aminopeptidase N carries an apical sorting signal and that it is localized on the ectodomain of the enzyme.     

Monoclonal antibodies to rabbit liver cytochrome P-448

Cytochrome P-448 (mol wt 55,000 Daltons) from rabbit liver was purified to a specific content of 16.6 nmol/mg. Mice were immunised with this preparation, their spleens removed and dissociated lymphocytes hybridised with myeloma cells. Four monoclonal antibodies against cytochrome P-448 were raised and partially characterised. All four antibodies interacted with cytochrome P-448 in intact microsomal fractions and selectively immunoadsorbed cytochrome P-448 from solubilised microsomal preparations. One of the antibodies inhibited benzo[a] pyrene hydroxylase activity in a reconstituted system, one had no effect on activity and two increased activity. The possible applications of such antibodies are discussed.