Nearshore abundance of zooplankton in relation to shoreline configuration and mechanisms involved

Zooplankton abundance was examined in relation to shorelineconfiguration. Four embayments (0.15, 1.5, 4 and 7 km opening)were each divided into three zones, corresponding to regionsinside, outside and downstream. A portion of straight coast[{small tilde}12 km, Sainte-Flavie (SF)] was also divided intothree zones. Only the largest embayment was sampled in 1993,but all embayments and SF were sampled in 1994. In 1993, zooplanktonabundance was significantly higher within the embayinent thanin external zones for six of seven dates. Zones inside the fourembayments had generally higher zooplankton abundance than zonesexternal to the embayments in 1994, but the opposite was observedduring the first of two sampling dates for the largest embayments.No definite pattern was observed among zones along SF. Fourhypotheses could explain the higher abundance of zooplanktoninside embayments. Three were tested using meroplankton (M)/holoplankton(H) ratios. The M/H ratios confirmed hypotheses of retentionand local production of meroplanktonic larvae inside embayments.Zooplankton abundance was lower inside than in zones externalto embay ments only twice, and wind direction may have beenresponsible for these results. No embayment size effect on zooplanktonabundance was detected. The patchy distribution of zooplanktonmay increase the difficulty of observing an effect of embaymentsize on zooplankton abundance.     

Protein synthesis in relation to ripening of pome fruits

Protein synthesis by intact Bartlett pear fruits was studied with ripening as measured by flesh softening, chlorophyll degradation, respiration, ethylene synthesis, and malic enzyme activity. Protein synthesis is required for normal ripening, and the proteins synthesized early in the ripening process are, in fact, enzymes required for ripening. ¹⁴C-Phenylalanine is differentially incorporated into fruit proteins separated by acrylamide gel electrophoresis of pome fruits taken at successive ripening stages. Capacity for malic enzyme synthesis increases during the early stage of ripening. Fruit ripening and ethylene synthesis are inhibited when protein synthesis is blocked by treatment with cycloheximide at the early-climacteric stage. Cycloheximide became less effective as the climacteric developed. Ethylene did not overcome inhibition of ripening by cycloheximide. The respiratory climacteric is not inhibited by cycloheximide. It is concluded that normal ripening of pome fruits is a highly coordinated process of biochemical differentiation involving directed protein synthesis.     

Fluorescence Changes in Nerve Induced by Stimulation : Their relation to protein configuration

It was previously assumed, on the basis of changes in the ultraviolet absorption spectrum and of increase in ionizable sulfhydryl groups, that during excitation the proteins of excitable structures undergo some structural rearrangements, and these rearrangements may be similar to those designated by the term transconformation. In the present experiments, it was observed that electrical stimulation of peripheral nerves from rat, guinea pig, frog, and crab causes a decrease in their fluorescence. The peaks of the emission and activation spectra correspond to those attributed to proteins. Denaturing agents, such as urea, were also found to decrease the fluorescence of nerve extracts. It is, therefore, probable that the decrease in fluorescence, associated with the excited state, is due to a change in the configuration of the nerve proteins. The fluorescent method is applicable not only to tissue extracts but allows the observation of surviving nerve fibers before, during, and after stimulation. It showed that fluorescence of the fibers decreases invariably during stimulation and tends to return to the control level during restoration. The reduction in fluorescence is quantitatively related to the number of stimuli received by the nerve.     

Regulation of lipid synthesis in relation to keratinocyte differentiation capacity

Cultured keratinocytes and squamous carcinoma cells provide a useful model system for studying the processes involved in the regulation of differentiation, as the differentiation capacity of the cells can be modulated experimentally by changing the extracellular calcium concentration. Furthermore, the squamous carcinoma cell lines exhibit a defect in their differentiation capacity which they express to different extents. In this paper, the effect of external lipoproteins has been studied on lipid synthesis in normal keratinocytes and three squamous carcinoma cell (SCC) lines which showed a decreasing capacity to differentiate in the order of normal keratinocytes greater than SCC-12F2 greater than SCC-15 greater than SCC-4. The ability of the cells to form cornified envelopes was taken as a measure of differentiation capacity. The rate of total lipid synthesis as well as the phospholipid-neutral lipid ratio decreased in the order SCC-4 greater than SCC-15 greater than SCC-12F2 greater than or equal to normal keratinocytes, clearly correlating with the differentiation capacity of the cells. Because of the high rate of phospholipid synthesis and the low rate of ceramide synthesis, it is concluded that, under these in vitro conditions used, the maturation of keratinocytes proceeds to a lesser extent than that seen under in vivo conditions. In proliferating cells, in which the low-density lipoprotein (LDL) receptor is operative to a high extent, the rate of lipogenesis, especially that of neutral lipids, responded dramatically to changes of extracellular lipoprotein concentration. In the presence of lipoproteins a marked decrease of cholesterol and triacylglycerol synthesis and an increase of cholesterol ester synthesis has been observed. On the other hand, in differentiating cells lipogenesis appeared to be independent of extracellular lipoproteins, due to the absence of the LDL uptake mechanism, the only exception being the synthesis of triacylglycerols, the rate of which could be modulated to a certain extent by extracellular lipoproteins. The results presented here demonstrate a close inverse relationship between the regulation of lipogenesis by extracellular lipoproteins and the ability of the cells to differentiate.     

Population dynamics of tundra voles in relation to configuration of willow thickets in southern arctic tundra

The areal extent and configuration of thickets of willow shrubs are currently changing in the Arctic both as an effect of global warming and changed browsing pressure of reindeer. These changes have been predicted to impact the distribution and abundance of wildlife species relying on willow thickets as habitat. We assessed the relation between variables quantifying willow thicket configuration and population dynamics of tundra voles (Microtus oeconomus) in three riparian regions in Finnmark, northern Norway, which were subject to intense browsing by semi-domesticated reindeer. The tundra vole, which exhibits 5-year population cycles in Finnmark, is the dominant small rodent species in riparian landscape elements in southern arctic tundra. In the course of a 4-year trapping study, tundra vole populations went through the cyclic phases of increase, peak and crash, however, with distinct differences between the three regions in the population dynamics. Within regions, the occupancy pattern during the increase phase was positively related to willow thicket configuration (in particular edge density and willow height) only in the region attaining the highest abundance and occupancy. However, local abundance was not clearly related to habitat features within any regions. The lack of consistency in the response of tundra vole populations to willow thicket configuration, as well as the positive relation between the degree of thicket shredding and tundra vole habitat occupancy in one of the regions, indicates that tundra voles will not be much affected by climate or browsing induced changes in the shrubbiness of the tundra in the future.     

Stereospecific synthesis and absolute configuration of mexiletine

Data on the absolute configuration of mexiletine (MEX) do not appear to have been published, although in several published reports the configuration is referred to as (?)-(R) and (+)-(S), based on information from manufactures providing the drug stereoisomers. We demonstrate that (?)-MEX has the (R)-configuration by mean of a new stereospecific synthesis. X-Ray analysis of an optical active sample of (+)-MEX as its hydrobromide salt, obtained from chemical resolution of the racemic mixture, was carried out in order to obtain precise information on bond lengths and angles, useful for studies on structure–activity relationships. We also report the NMR analysis in presence of Eu(hfc)₃ as shift reagent, which represents a simple method for the determination of enantiomeric excess (ee) in addition to the well-known chiral HPLC methods. © 1994 Wiley-Liss, Inc.     

Acetyl transfer in arylamine metabolism

1. N-Hydroxyacetamidoaryl compounds (hydroxamic acids) are metabolites of arylamides, and an enzyme that transfers the acetyl group from these derivatives to arylamines has been found in rat tissues. The reaction products were identified by thin-layer chromatography and a spectrophotometric method, with 4-amino-azobenzene as acetyl acceptor, was used to measure enzyme activity. 2. The acetyltransferase was in the soluble fraction of rat liver, required a thiol for maximum activity and had a pH optimum between 6·0 and 7·5. 3. The soluble fractions of various rat tissues showed decreasing activity in the following order: liver, adrenal, kidney, lung, spleen, testis, heart; brain was inactive. 4. With the exception of aniline and aniline derivatives all the arylamines tested were effective as acetyl acceptors but aromatic compounds with side-chain amino groups were inactive. 5. The N-hydroxyacetamido derivatives of 2-naphthylamine, 4-amino-biphenyl and 2-aminofluorene were active acetyl donors but N-hydroxyacetanilide showed only slight activity. Acetyl-CoA was not a donor. 6. Some properties of the enzyme are compared with those of other acetyltransferases.