Metabolism of high density lipoprotein lipids by the rat liver: evidence for participation of hepatic lipase in the uptake of cholesteryl ester.

In order to determine the role of hepatic lipase in the hepatic uptake and metabolism of high density lipoprotein (HDL) triglycerides, cholesteryl esters, and phospholipids, isolated rat livers were perfused with a reconstituted HDL (rHDL) radiolabeled with [3H]triolein and [14C]cholesteryl oleate or palmitoyl-[14C]linoleoyl phosphatidylcholine. A bolus of radiolabeled rHDL was injected into the portal vein and livers were perfused for 5 min using a nonrecirculating perfusion system. Recovery of rHDL triolein in the liver as intact triolein was used to determine the amount of unmetabolized rHDL remaining in the liver. After correcting for the amount of unmetabolized rHDL remaining in the liver, about 30% of the rHDL triolein was hydrolyzed of which 19% was recovered in the liver and 11% in the perfusate. Moreover, about 7% of the rHDL phosphatidylcholine was hydrolyzed to lysophosphatidylcholine, all of which was recovered in the perfusate. Although there was no hydrolysis of rHDL cholesteryl oleate, about 30% of the cholesteryl oleate was taken up by the liver. Preperfusion of the liver with heparin to deplete the liver of hepatic lipase resulted in about a 70% reduction in rHDL triolein hydrolysis and about a 75% reduction in rHDL cholesteryl oleate uptake. Although hepatic lipase hydrolyzes both triglycerides and phosphatidylcholines, elimination of the triolein from rHDL had no effect on the uptake of rHDL cholesteryl oleate, but replacement of the rHDL phosphatidylcholine with a nonhydrolyzable phosphatidylcholine diether resulted in an 87% reduction in cholesteryl oleate uptake. These results indicate that hepatic lipase is necessary for the hepatic uptake of both HDL triglycerides and cholesteryl esters and that the uptake of cholesteryl esters is not dependent on the hydrolysis of HDL triglycerides but is dependent on the hydrolysis of HDL phospholipids.     

Levels of tropinone-reductase activities influence the spectrum of tropane esters found in transformed root cultures of Datura stramonium L.

The nortropane sulphur analogues 8-thiabicyclo[3.2.1] octan-3-one, 8-thiabicyclo[3.2.1]octan-3a-ol and 8-thiabicyclo[3.2.1]octan-3-ol have been found to have differential effects in vitro on the activities of tropinone reductase I and tropinone reductase II from Datura stramonium L. It has been demonstrated that only tropinone reductase I is able to metabolise 8-thiabicyclo[3.2.1]octan-3-one and that only this enzyme is inhibited by 8-thiabicyclo[3.2.1]octan-3-ol and 8-thiabicyclo[3.2.1]octan-3-ol. A K _m of 0.035 mM was determined for 8-thiabicyclo[3.2.1]octan-3-one and I₅₀ values of 0.081 mM and 0.021 mM for 8-thiabicyclo[3.2.1]octan-3-ol and 8-thiabicyclo[3.2.1]octan-3-ol, respectively. The influence that these differential interactions might have on metabolism was investigated in transformed root cultures of D. stramonium. It was found that when these cultures were grown in the presence of either 8-thiabicyclo[3.2.1]octan-3-one or 8-thiabicyclo[3.2.1]octan-3-ol the spectrum of alkaloids that accumulated was altered from that found in control roots in the manner predicted from the observed effects of these inhibitors on the isolated reductases. The effect could be mimicked by feeding pseudotropine, the product of tropinone reductase II. It is concluded that the relative levels of activity of the two tropinone reductases might play an important role in regulating the balance of tropan-3-ols to tropan-3-ols seen in the spectrum of tropane-alkaloid-producing plants.Abbreviations GC/MS gas chromatography/mass spectrometry; - I₅₀ concentration of inhibitor required to reduce the rate of reaction to half the maximal value; - -TBOL 8-thiabicyclo[3.2.1]octan-3-ol; - -TBOL 8-thiabicyclo[3.2.1]octan-3-ol; - TBON 8-thiabicyclo[3.2.1]octan-3-one; - TR tropinone reductase We are most grateful to J. Eagles (I.F.R., Norwich) for GC/MS analysis, to colleagues at I.P.B.P. and I.F.R. for helpful discussions, to the technical staff (Chemistry, Glasgow) and to W. Millar (Chemistry, Glasgow) for assistance with the reduction of TBON. This work was, in part, supported by a grant to B Dräger from the Deutsche Forschungsgemeinschaft (Dr227/I-I). The research reported here was supported by an Academic Research Collaboration Cooperative Award (project No. 215) from the British Council and the Deutscher Akademischer Austauschdienst to R.J. Robins and B. Dräger.     

Two frameshift mutations in the cystic fibrosis gene

Cystic fibrosis (CF) is a recessive disease caused by mutations in the CF transmembrane conductance regulator (CFTR) gene. We have identified in exon 7 two frameshift mutations, one caused by a two-nucleotide insertion and the other caused by a one-nucleotide deletion; these mutations--CF1154insTC and CF1213delT, respectively, are predicted to shift the reading frame of the protein and to introduce UAA(ochre) termination codons at residues 369 and 368.     

Multiple components of a complex androgen-dependent enhancer.

Sex-limited protein (Slp) is expressed in adult male mice. A 160-basepair fragment 2 kilobases upstream of the gene serves as an androgen-dependent enhancer of chloramphenicol acetyltransferase expression in transient transfection assays in cells with endogenous or cotransfected androgen receptor. One element that is necessary, but not sufficient, for induction is a consensus glucocorticoid (or hormone) response element (HRE). This element binds to the mouse androgen receptor in vitro, but with apparent weak affinity. Induction by the HRE is greatly augmented by an accessory sequence within the 160 basepairs, suggesting that cooperative interactions confer strong response to androgen. Additional elements within the enhancer modulate induction, positively or negatively, and exhibit cell-specific behavior. Of particular interest are two degenerate HREs that are adjacent to the consensus sequence; they show no independent activity, but are functionally significant in conjunction with other elements. The complexity of this enhancer may reflect biological mechanisms that ensure specificity of hormonal response and allow gene expression to respond to changes in hormone concentration.     

MULTIVARIATE PHENOTYPIC DIFFERENTIATION AMONG BOTTLENECK LINES OF THE HOUSEFLY

Multivariate phenotypic differentiation in eight morphometric traits was examined in bottleneck lines of the housefly initiated with one, four, or 16 pairs of flies from a natural outbred population. Differentiation was assessed using a Mahalanobis' distance metric in units of additive genetic variance and covariance estimated from the ancestral population (i.e., generalized genetic distance). This distance metric was partitioned into contributions of size and shape to total distance. Bottleneck lines of all sizes diverged significantly from the ancestral line, but the direction of these shifts differed among the lines of different initial founding size. Those populations founded with single pairs diverged from the ancestral line mostly in shape; the 16-pair lines differentiated almost entirely in size, and the four-pair lines were intermediate in the relative contribution of shape to differentiation from the control. Bottlenecks serve to alter the genetic relationships among traits within the derived populations and in doing so could promote speciation by permitting differentiation of the populations along evolutionary trajectories less accessible to the base population.     

Occurrence of Nitrate Reductase and Molybdopterin in Xanthomonas maltophilia

Fifteen of 23 ATCC strains and 2 of 9 clinical isolates of Xanthomonas maltophilia, all of which grew aerobically on ammonia, but not nitrate, as a sole nitrogen source, reduced nitrate to nitrite. X. maltophilia failed to grow anaerobically on complex medium with or without nitrate, so it is considered an obligate aerobe. Nitrate-reducing strains contained reduced methyl viologen nitrate reductase (MVH-NR) with specific activities ranging from 49.2 to 192 U mg of protein⁻¹. Strain ATCC 17666 doubled its cell mass after 3 h of growth on nitrate broth under low aeration, possessed maximal MVH-NR activity, and converted the added nitrate to nitrite, which accumulated. Dissolved oxygen above 15% saturation greatly suppressed nitrite formation. All strains, except ATCC 14535, possessed between 0.25 and 5.05 pmol of molybdopterin mg of protein⁻¹ as measured by the Neurospora crassa nit-1 assay. The molybdopterin activity in the soluble fraction sedimented as a single symmetrical peak with an s_20,w of 5.1. Studies identified MVH-NR in selected strains as a membrane-bound protein. The deoxycholate-solubilized MVH-NR sedimented as a single peak in sucrose density gradients with an s_20,w of 8.8. The MVH-NR of X. maltophilia has the physical characteristics of a respiratory nitrate reductase and may enable cells to use nitrate as an electron sink under semiaerobic conditions.     

Current Productivity and Prehistoric Use of Piñon (Pinus edulis,Pinaceae) in the Dolores Archaeological Project Area,Southwestern Colorado

The possible contribution of pinon (Pinus edulis) seed to the diet of an Anasazi population is investigated using present data on seed productivity and archaeological data on resource use. Annual estimates of total productivity for a 135.7 sq km study area in Montezuma County, Colorado, vary by a factor of 141 in a sample spanning 5 yr. Trees greater than about 25 cm (basal diameter) are usually monoecious and produce significantly more cones per tree but fewer good seeds per cone than smaller, usually dioecious specimens. Archaeological data suggest that piñon seed was a relatively unimportant food item after the initial period of Anasazi colonization of the Dolores River valley about a.D. 600. Use of piñon seed as food was inversely related to degree of agricultural intensification and use of piñon for fuel.     

Three-dimensional growth and morphogenesis of mouse submandibular epithelial cells in serum-free primary culture

Mouse submandibular epithelial cells can be grown in primary culture using the collagen gel matrix and a chemically defined medium consisting of insulin, transferrin, cholera toxin, and BSA (or FGF). Sustained cell growth leading to a 5–10-fold increase in cell number was observed in less than 2 weeks. In the presence of these additives, clumps of cells proliferate by extending ‘star-like’ projections into the matrix, resulting in three-dimensional outgrowths. The morphology of these outgrowths can be modulated to form a ‘cyst-like’ appearance by deleting BSA and adding cortisol to the basal medium containing insulin, transferrin, cholera toxin and FGF. In brief, a serum-free medium for sustained growth has been devised and a simple manipulation of supplements can modulate the three-dimensional colony morphology in the collagen gel matrix. Finally, the resulting outgrowths can produce epidermal growth factor (EGF) in response to dihydrotestosterone.