Identification of a short sequence essential for actin binding by Dictyostelium ABP-120

Tryptic digestion of ABP-120, an actin cross-linking protein from Dictyostelium discoideum, generates a ladder of peptides differing in molecular mass by 13,000 daltons, indicating a structural repeat within the molecule. A number of peptides bind actin with the smallest having a molecular mass of 17,000 daltons (T17). Our sedimentation assays also show that a peptide of 14,000 daltons does not bind actin. Using the full-length cDNA sequence (Noegel, A., Rapp, S., Lottspeich, F., Schleicher, M., and Stewart, M. (1989) J. Cell Biol. 109, 607-618) and protein sequencing techniques, we have determined that T17 begins at residue 89 while T14 begins at residue 116. Therefore we have localized 27 amino acids which are essential for actin binding activity. This region is at the end of the molecule, distal from the repetitive beta-sheet region predicted from the cDNA sequence, and displays high sequence identity with regions in the N termini of ABP/filamin, dystrophin, beta-spectrin, and alpha-actinin.     

Lifespan extension in genetically modified mice

Major advances in aging research have been made by studying the effect of genetic modifications on the lifespan of organisms, such as yeast, invertebrates (worms and flies) and mice. Data from yeast and invertebrates have been the most plentiful because of the ease in which genetic manipulations can be made and the rapidity by which lifespan experiments can be performed. With the ultimate focus on advancing human health, testing genetic interventions in mammals is crucial, and the mouse has proven to be the mammal most amenable to this task. Lifespan studies in mice are resource intensive, requiring up to 4 years to complete. Therefore, it is critical that a set of scientifically-based criteria be followed to assure reliable results and establish statistically significant findings so other laboratories can replicate and build on the data. Only then will it be possible to confidently determine that the genetic modification extends lifespan and alters aging.     

Testing Quasi-Independence in Stratified Triangular Contingency Tables

A special class of incomplete contingency tables has structural zeroes in one or more cells. Some of these tables have a triangular appearance in the sense that they are square and their cells are known a priori to contain zeroes above (or below) their main diagonals. We propose methods of analyzing log-linear models and testing quasi-independence in these triangular tables. We also offer a method for combining such tables that are stratified by a concomitant categorical variable. This strategy follows the same approach used in a Cochran-Mantel-Haenszel test.     

Improved Bioreaction Kinetics for the Simulation of Continuous Ethanol Fermentation by Saccharomyces cerevisiae

A kinetic model for the production of ethanol by Saccharomyces cerevisiae has been developed from semiempirical analysis. The values for the parameters in this model were then determined by nonlinear multiple regression using the data of Bazua and Wilke ( 1977). The final equations were μ=0.427s(1-(p/101.6)^1.95)/(0.245+s), Y_X/p=0.291, and Y_X/s=0.152(1-p/302.3). This model was then used to simulate a continuous stirred tank fermentor (CSTF) and compared to other models using the same experimental data but different kinetics. The equations required to use these kinetics in a CSTF with recycle were then developed. From this simulation, it was found that, for a CSTF with recycle, the best configuration to operate is an external recycle, with a low bleed and recycle ratio.     

CYTOCHROME c548 IN NOSTOC SP. (CYANOPHYCEAE): AN ELECTRON ACCEPTOR FROM REDUCED NADP IN THE DARK1

A c-type, carbon monoxide-binding cytochrome was isolated and studied from an endophytic Nostoc sp. Enzymatic transfer of electrons from NADPH to this cytochrome was demonstrated in cell-free preparations under dark, anaerobic conditions, probably mediated by NADPH-cytochrome reductase or ferredoxin-NADP reductase present in the extracts. This cytochrome, with an α-peak at 548 nm, had physicochemical properties similar to the low potential c-type cytochrome, cytochrome c₅₄₉, previously described by other workers from Anacystis nidulans. The participation of such c-cytochromes in dark electron transport, possibly respiratory, of bluegreen algae is strongly indicated.     

The substrate specificity of bovine and feline lysosomal alpha-D-mannosidases in relation to alpha-mannosidosis

Lysosomal alpha-mannosidases were partially purified from bovine and feline liver and employed to digest a large number of oligosaccharides with structures corresponding to the oligomannosyl parts of complex, hybrid, and high-mannose glycans. The incubation products were identified by high pressure liquid chromatography with reference compounds of defined structure and by acetolysis. For all classes of substrates, the lysosomal alpha-mannosidases displayed a high degree of in vitro specificity with regard to the hydrolysis of mannose residues. Thus, in each case, 1 or at most 2 residues were always preferentially cleaved so that the degradative process proceeded down a well defined pathway. A comparison of the relative efficiency with which lysosomal alpha-mannosidases catalyzed the hydrolysis of particular oligosaccharides and of the structures of the resulting intermediates with those of the compounds accumulated in alpha-mannosidosis allows conclusions to be drawn regarding the nature of the enzymatic defect. In bovine alpha-mannosidosis, the oligosaccharides are those expected for a partial deficiency of normal lysosomal alpha-mannosidase, so that they correspond to intermediates in the normal catabolic pathway. In feline alpha-mannosidosis, in which the alpha-mannosidase deficiency is more severe than in cattle, the accumulated oligosaccharides primarily represent intact oligomannosyl moieties of N-linked glycans rather than the products of residual alpha-mannosidase activity.