Feedback inhibition of polyisoprenyl pyrophosphate synthesis from mevalonate in vitro. Implications for protein prenylation.

The prenylation of proteins utilizes the polyisoprenyl pyrophosphates (FPP) and geranylgeranyl pyrophosphate (GGPP) as prenyl donors. These polyisoprenoids are also precursors to ubiquinone and dolichol synthesis. We have previously described the geranylgeranylation of rab 1b from labeled mevalonate in rabbit reticulocyte lysates (Khosravi-Far, R., Lutz, R. J., Cox, A. D., Conroy, L., Bourne, J. R., Sinensky, M., Balch, W. E., Buss, J. C., and Der, C. J. (1991) Proc. Natl. Acad. Sci. U.S.A. 88, 6264-6268). We now directly demonstrate the incorporation of mevalonate into FPP and GGPP in rabbit reticulocyte cytosol. High pressure liquid chromatography analysis reveals that only all-trans-E,E,E-GGPP, the prenyl donor for in vivo protein geranylgeranylation, is synthesized. Incubations with recombinant H-ras and rab1b result in an increased synthesis of farnesyl and geranylgeranyl derivatives, respectively. The increase is wholly accounted for by protein-incorporated polyisoprenoids with no change in the polyisoprenyl pyrophosphate pools. Further, GGPP inhibits its own synthesis, without affecting FPP synthesis, with half-maximal inhibition at approximately 3 microM GGPP. Inhibition of FPP synthesis by the inhibition of isopentenyl isomerase causes a dramatic increase in isopentenyl pyrophosphate synthesis. FPP also inhibits conversion of mevalonate into FPP. These findings indicate that these polyisoprenyl pyrophosphates can down-regulate their own synthesis in vitro, and this regulation may control the levels of these polyisoprenoids in vivo.     

Negative density-dependent emigration of males in an increasing red deer population

In species with polygynous mating systems, females are regarded as food-limited, while males are limited by access to mates. When local density increases, forage availability declines, while mate access for males may increase due to an increasingly female-biased sex ratio. Density dependence in emigration rates may consequently differ between sexes. Here, we investigate emigration using mark-recovery data from 468 young red deer Cervus elaphus marked in Snillfjord, Norway over a 20-year period when the population size has increased sixfold. We demonstrate a strong negative density-dependent emigration rate in males, while female emigration rates were lower and independent of density. Emigrating males leaving the natal range settled in areas with lower density than expected by chance. Dispersing males moved 42 per cent longer at high density in 1997 (37 km) than at low density in 1977 (26 km), possibly caused by increasing saturation of deer in areas surrounding the marking sites. Our study highlights that pattern of density dependence in dispersal rates may differ markedly between sexes in highly polygynous species. Contrasting patterns reported in small-scale studies are suggestive that spatial scale of density variation may affect the pattern of temporal density dependence in emigration rates and distances.     

Modellversuche zur überlebensdauer von Erwinia amylovora im Verdauungstrakt der Honigbiene,im Honig und an Teilen des Bienenstocks

An lagerndem Winterknoblauch ist unter außenluft‐(x + 6, 5 bzw. 8, 3 °C) und maschinengekühlten Bedingungen (x‐1 . . .‐2 °C) in zwei Lagerperioden die Entwicklung der einzelnen Fäuleerreger verfolgt und in Abhängigkeit von der Lagerdauer statistisch quantifiziert worden. An Hand des Masseanteiles befallener Zwiebeln und der Befallsintensität wird eine zunehmende Ausbreitung von Penicillium spp. und einer Gruppe mit Befall durch mehrere Fäuleerreger unter beiden Lagerbedingungen und von einer Botrytis‐Species (vermutlich B. porri Buchw.) im maschinengekühlten Lager belegt. Fäuleverluste durch Helminthosporium allii Campanile und Bakterien zeigen dagegen mit fortschreitender Lagerdauer einen abnehmenden Verlauf. Mit Eintreten von lagerungsbedingter Seneszenz steigen die Verluste progressiv an. Kaltlagerbedingungen verzögern dagegen ihre Ausbreitung. Die Verluste durch alle Fäulerreger (Fäule gesamt) zeigen eine gleichmäßige Zunahme während der Lagerdauer.     

Porcine-specific hemoglobin saturation measurements.

The determination of O(2) consumption by using arteriovenous O(2) content differences is dependent on accurate oxyhemoglobin saturation measurements. Because swine are a common experimental species, we describe the validation of CO-oximeter for porcine-specific oxyhemoglobin saturation. After developing a nonlinear mathematical model of the porcine oxyhemoglobin saturation curve, we made 366 porcine oxyhemoglobin saturation determinations with a calibrated blood-gas analyzer and a porcine-specific CO-oximeter. There was a high degree of correlation with minimal variability (r(2) = 0.99, SE of the estimate = 5.2%) between the mathematical model and the porcine-specific CO-oximeter measurements. Bland-Altman comparison showed that the CO-oximeter measurements were biased slightly lower (-0.4 vol%), and the limits of agreement (+/-2 SD) were 0.7 and -1.5 vol%. This is in contrast to a 10-20 vol% error if human-specific methods were used. The results show excellent agreement between the nonlinear model and CO-oximeter for porcine-specific oxyhemoglobin saturation measurements. In contrast, comparison of the porcine-specific oxyhemoglobin saturations with saturations obtained by using human methods highlights the necessity of species-specific measurement methodology.     

Aminopeptidasen von Basidiomyceten

Zusammenfassung Die Spezifität von Aminopeptidasen (AP) aus den Basidiomyceten Hapalopilus nidulans und Pleurotus ostreatus gegenüber Peptiden wurde durch dünnschichtchromatographische Analyse der Spaltprodukte getestet.Im ganzen hat sich gezeigt, daß Substratspezifitäten, welche durch Aminosäure-Arylamide ermittelt wurden, nicht ohne weiteres auch für Peptide gelten. Zumindest kann aber mit diesen künstlichen Substraten untersucht werden, ob eine Peptidase einem bestimmten Grundtyp zugehört. Diese scheinen sich bei den verschiedenen Mikroorganismen weitgehend zu gleichen.Das (Leucin)aminopeptidase-artige Enzym AP.4 aus H. nidulans, welches ein Tetramer aus den kleineren Untereinheiten AP. I/II darstellt, hat qualitativ die gleiche Spezifität wie diese, jedoch ist sie quantitativ von Di-zu Tripeptiden verschoben.AP.53 aus P. ostreatus, die nach Verhalten in der Elektrophorese und gegenüber Arylamiden mit AP.I/II homolog scheint, weist auch nahezu dasselbe Substratspektrum auf.Die mit künstlichen Substraten ermittelte Spezifität der (Prolin) iminopetidase (AP.5) aus H. nidulans hat sich auch in diesen Untersuchungen bestätigt: Sie ist im wesentlichen auf prolinhaltige Peptide beschränkt.

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Aminopeptidases of basidiomycetesII. Comparison of substrate specificities: (Proline)iminopeptidase and (Leucine)aminopeptidase of Hapalopilus nidulans —Aminopeptidase 53 of Pleurotus ostreatus

Summary The specificity of aminopeptidases (AP) of the basidiomycetes Hapalopilus nidulans and Pleurotus ostreatus was tested for enzymatic hydrolysis of peptides by thin layer chromatography.The data show that specificities towards aminoacid arylamides cannot necessarily be attributed to natural peptides. These artificial substrates may be used, however, to determine the type of aminopeptidases seemingly similar to all microorganisms.The (leucine)aminopeptidase AP.4 of H. nidulans which is the tetramer composed on the smaller subunits AP. I and AP. II has qualitatively the same substrate specificity as its monomers. Qualitatively the larger enzyme cleaves tripeptides better than dipeptides, whereas the subunits are more effective in hydrolysing dipeptides.Because of its behaviour towards aminoacid naphtylamides and its electrophoretic mobility, AP.53 of P. ostreatus seems homologous to AP. I/II of H. nidulans. The substrate specificity towards peptides confirms this assumption.The specificity of AP. 5 (proline iminopeptidase) which was earlier investigated using artificial substrates has now been corroborated with natural peptides.