Effects of bilayer thickness on the activity of diacylglycerol kinase of Escherichia coli.

We have developed a procedure for the reconstitution of Escherichia coli diacylglycerol kinase (DGK) into phospholipid bilayers containing diacylglycerol substrate. When DGK is reconstituted into a series of phosphatidylcholines containing monounsaturated fatty acyl chains, activity against dihexanoylglycerol (DHG) as a substrate was found to be markedly dependent on the fatty acyl chain length with the highest activity in dioleoylphosphatidylcholine [di(C18:1)PC] and a lower activity in bilayers with shorter or longer fatty acyl chains. Low activities in the short chain phospholipid dimyristoleoylphosphatidylcholine [di(C14:1)PC] followed from an increase in the K(m) value for DHG and ATP, with no effect on v(max). In contrast, in the long chain lipid dierucoylphosphatidylcholine [di(C24:1)PC], the low activity followed from a decrease in v(max) with no effect on K(m). In mixtures of two phosphatidylcholines with different chain lengths, the activity corresponded to that expected for the average chain length of the mixture. Cholesterol increased the activity in di(C14:1)PC but slightly decreased it in di(C18:1)PC or di(C24:1)PC, effects that could follow from changes in bilayer thickness caused by cholesterol.     

The kit ligand encoded at the murine Steel locus: a pleiotropic growth and differentiation factor

The c-kit receptor and its recently identified ligand are allelic with the murine White Spotting and Steel loci, respectively. These observations brought to light the functions of the c-kit receptor system in melanogenesis, gametogenesis and hematopoeisis during embryogenesis and in postnatal life. The recent molecular analysis of several White Spotting and Steel alleles has provided insights into the mechanism of c-kit ligand-mediated processes, including cell proliferation, cell migration and cell survival. Furthermore, the availability of the kit ligand has allowed in vitro investigations of the pleiotropic functions of c-kit in development and cell differentiation to be carried out.     

Transfer and expression of the tetracyclin resistance transposon Tn925 in Acetobacterium woodii

The Enterococcus faecalis conjugative plasmid pCF10 was used to introduce Tn925 into Acetobacterium woodii by filter mating. Tetracycline resistance was transferred at frequencies of about 10(-6) per donor, but no plasmid DNA was found in the transconjugants. DNA hybridization analyses of HindIII-digested chromosomal DNA demonstrated the insertion of Tn925 at a variety of locations, whereas wild type DNA showed no hybridization at all. The transconjugants were used as donor in mating experiments with tetracycline-sensitive Bacillus subtilis. Transfer of tetracycline resistance was observed at frequencies of 10(-8) per recipient.     

Morphological gradients in the starling basilar papilla

The starling cochlea was studied with TEM at four locations along the basilar papilla to investigate gradients in morphological features over the papilla's length and width. Hair cell shape changes continuously from neural to abneural and from basal to apical. Unlike the situation in mammals, there are no distinct populations of hair cells; the previously described types (tall hair cells and short hair cells) are merely extremes in a continuum. Contacts between THC are a normal feature. Except at the base of the papilla, SHC have very large cuticular plates, suggesting a micromechanical function for these cells. In contrast to the THC, the SHC normally completely lack afferent innervation; this indicates that their function is restricted to within the basilar papilla itself. © 1992 Wiley-Liss, Inc.     

Flavonoid systematics of ten sections of Ludwigia (Onagraceae)

Data for the flavonoids of 19 species in 10 sections of Ludwigia are presented. Eight flavonoids, comprising four glycoflavones, of which vitexin and isovitexin are reported for the first time in Ludwigia, and four flavonol glycosides, based on quercetin, are present in these species. Each section treated here has either glycoflavones or flavonols; presence of only onte class is considered to be advanced in the genus as a whole, compared with the presence of both glycoflavones and flavonols in the more generalized sects Myrtocarpus Cinerascentes, and Pterocaulon, which were examined earlier. Only glycoflavones are present in sects Macrocarpon (four species), Seminuda (five species), the ditypic African sect. Africana, the monotypic African sects Brenania, Cryptosperma, and Prieurea, the monotypic east Asian sect. Nipponia, and the monotypic pantropical section Fissendocarpa. Only flavonols are present in the monotypic Old Wodd section Caryophylloidea and sect. Oligospermum, which comprises nine species widespread in the OId and New Worlds.     

Effects of urbanization on streams of the Melbourne region, Victoria, Australia. I. Benthic macroinvertebrate communities

1. Macroinvertebrate community composition was assessed in small streams of the Melbourne region to test the effects of (a) urban density (catchment imperviousness 0–51%) and (b) stormwater drainage intensity (comparing the intensively drained metropolitan area with urban areas of the hinterland, which had open drains and some localized stormwater drainage).
2. Hinterland communities separated into two groups of sites correlating strongly with patterns of electrical conductivity (EC), basalt geology and annual rainfall. Community composition varied little in the high-EC, western group (imperviousness 0.2–1.2%), but in the eastern group it was strongly correlated with catchment imperviousness (0–12%), with lower taxon richness in more impervious catchments.
3. Metropolitan communities (imperviousness 1–51%) were all severely degraded, with high abundances of a few tolerant taxa. Community composition was poorly correlated with patterns of geology, rainfall or imperviousness. Differences between metropolitan and hinterland communities were well explained by patterns of biochemical oxygen demand and electrical conductivity, which were postulated to indicate the more efficient transport of pollutants to receiving streams by the metropolitan stormwater drainage system.
4. Degradation of macroinvertebrate community composition was well explained by urban density but intensive urban drainage increased degradation severely at even low urban densities. Quantification of relationships between imperviousness, drainage intensity and stream degradation can better inform the assessment, conservation and restoration of urban streams.