HERSIM: a microcomputer program designed to compute the limits of conversion for real homogeneous isothermal enzymic reactors

HERSIM is a program written in BASIC designed to aid the investigatorinterested in determining the substrate conversion in a realhomogeneous isothermal enzymic reactor, for various kineticequations. The program runs after tracer data relative to aDirac impulse to the reactor have been entered, and computesthe two limits of real conversion: total segregation and maximummixedness. The kinetic constants of the reacting system areinput as data, and the variation of conversion with reactortemperature between given limits is computed as accurately asrequested. Received on November 6, 1986; accepted on March 4, 1987     

Synthesis of 1-[3-deoxy-β-D-psicofuranosyl]uracil and related compounds

D-Fructose affords on treatment with cyanamide 2-amino-beta-D-fructofuro[2',3':3,4]-oxazoline which is not isolated but transformed directly by the reaction with ethyl propiolate into O(2,3)-anhydro-2-[beta-D-fructofuranosyl]uracil. This compound is benzoylated to the 1',4',6'-tri-O-benzoyl derivative by the action of benzoyl cyanide and triethylamine. On treatment with hydrogen chloride/dimethylformamide, the latter intermediate is converted to the 1-[1,4,6-tri-O-benzoyl-3-chloro-3-deoxy-beta-D-psicofuranosyl]uracil 1',4',5'-tribenzoate from which the title nucleoside derivative is obtained by methanolysis.     

Redox intermediates of Desulfovibrio gigas [NiFe] hydrogenase generated under hydrogen. M?ssbauer and EPR characterization of the metal centers

The hydrogenase (EC 1.2.2.1) of Desulfovibrio gigas is a complex enzyme containing one nickel center, one [3Fe-4S] and two [4Fe-4S] clusters. Redox intermediates of this enzyme were generated under hydrogen (the natural substrate) using a redox-titration technique and were studied by EPR and M?ssbauer spectroscopy. In the oxidized states, the two [4Fe-4S]2+ clusters exhibit a broad quadrupole doublet with parameters (apparent delta EQ = 1.10 mm/s and delta = 0.35 mm/s) typical for this type of cluster. Upon reduction, the two [4Fe-4S]1+ clusters are spectroscopically distinguishable, allowing the determination of their midpoint redox potentials. The cluster with higher midpoint potential (-290 +/- 20 mV) was labeled Fe-S center I and the other with lower potential (-340 +/- 20 mV), Fe-S center II. Both reduced clusters show atypical magnetic hyperfine coupling constants, suggesting structural differences from the clusters of bacterial ferredoxins. Also, an unusually broad EPR signal, labeled Fe-S signal B', extending from approximately 150 to approximately 450 mT was observed concomitantly with the reduction of the [4Fe-4S] clusters. The following two EPR signals observed at the weak-field region were tentatively attributed to the reduced [3Fe-4S] cluster: (i) a signal with crossover point at g approximately 12, labeled the g = 12 signal, and (ii) a broad signal at the very weak-field region (approximately 3 mT), labeled the Fe-S signal B. The midpoint redox potential associated with the appearance of the g = 12 signal was determined to be -70 +/- 10 mV. At potentials below -250 mV, the g = 12 signal began to decrease in intensity, and simultaneously, the Fe-S signal B appeared. The transformation of the g = 12 signal into the Fe-S signal B was found to parallel the reduction of the two [4Fe-4S] clusters indicating that the [3Fe-4S]o cluster is sensitive to the redox state of the [4Fe-4S] clusters. Detailed redox profiles for the previously reported Ni-signal C and the g = 2.21 signal were obtained in this study, and evidence was found to indicate that these two signals represent two different oxidation states of the enzyme. Finally, the mechanistic implications of our results are discussed.     

Immunocytochemical localization of the major glutathione S-transferases in adult Schistosoma mansoni

Indirect immunofluorescence was used to investigate the tissue distribution of the major isoenzymes of Schistosoma mansoni glutathione S-transferase (GSH S-transferase). When polyclonal rabbit antisera against GSH S-transferase isoenzymes SmGST-1, -02, and -3 were applied to cryostat or plastic-embedded sections of fixed adult worms, a punctate pattern of enzyme distribution was observed that was restricted to the parenchyma. Labeling was much more pronounced in males than females, consistent with the biochemically determined distribution of these enzymes between the sexes. Intense immunolabeling was noted within the subectocytoplasmic core tissue of the tubercles of the male that appeared to be connected to deep parenchymal cells by immunoreactive cell processes. Immunofluorescence could be blocked completely by prior incubation of antisera with affinity-purified enzyme. Although schistosome GSH S-transferases have been reported to be protective antigens, no immunoreactivity was detected within or on the tegument, including the dorsal spines of the male. The lack of tegumental immunoreactivity was confirmed by immunoblotting of tegumental membrane preparations following SDS-PAGE. Muscle fibers, vitelline cells, and cecal epithelium also failed to react. The fact that the GSH S-transferases were not uniformly distributed among all parenchymal cells suggests the existence of subpopulations of parenchymal cells that are preferentially involved in the conjugation of electrophiles with glutathione.     

Contractile properties of rat soleus muscle after 15 days of hindlimb suspension

The properties of the contractile elements interacting to develop force in atrophied rat soleus muscle were studied by using single skinned fibers, which permitted direct access to the contractile apparatus. Muscle atrophy was induced by 15 days of hindlimb suspension. Suspension resulted in a decrease of maximal tension relative to an important decline in fiber diameter. Ca affinity of the contractile proteins was not changed insofar as the tension-pCa relationship was not shifted along the pCa axis. However, after hindlimb suspension 1) the value of the Hill coefficient from the tension-pCa curve was found to be higher, 2) a higher Ca threshold for activation was reported, and 3) a significant increase in contraction kinetics was described. All these results suggested that after suspension the mechanical properties of the slow-twitch soleus appeared to resemble more closely those of a fast-twitch muscle. Our results were in complete agreement with published histochemical data.     

GROWTH PATTERN,REPRODUCTION, AND SELF-THINNING IN SEAWEEDS1

In unispecific plant stands, the logarithm of mean individual weight (w) depends on the logarithm of density (d) by the -3/4 power law (a slope of -1.5 and an intercept ranging from 2.3 to 5.0). The analysis of the w and d relationships in whole cohorts of two seaweed species from the Strait of Gibraltar shows deviations from the canonical equation. The kelp Phyllariopsis purpurascens (C. Agardh) Henry et South (Phaeophyta) growing at a 30-m depth has the lowest intercept value (0.6) recorded for any plant species and a slope not significantly different from -1.5. The slope value is in accordance with those found in species whose growth is not stopped by reproduction. Irradiance under a single layer of blades was lower than the photosynthetic light compensation point, and this could be due to overdispersion of the shoots and, in consequence, to the low intercept value of the self-thinning equation. The w to d relationships in Asparagopsis armata Harvey (Rhodophyta) show two different components: no dependence between these two variables (slope not significantly different from 0) at densities < 500 shoots·m^?2, and a slope more negative (-2.1) than proposed by the -3/2 power law at densities > 500 shoots·m^?2. The pattern at high densities could be due to intraspecific competition for light, whereas the slope ～0 at low densities could be related to inhibition of growth by reproduction (cystocarp and carpospore production). Therefore, rather than being considered exceptional, we suggest that a gradient of variability could be expected in the dependence of w on d when specific growth patterns and reproduction are considered.     

Small-scale association measures in epibenthic communities as a clue for allelochemical interactions

The small-scale associations in a rocky subtidal community in the northwestern Mediterranean were studied by a development of the continuous line transect method. This method allowed the overall measurement of non-randomness in interspecific contacts and the assignment of an association index to each species-pair, whose, significance was tested by Monte Carlo procedures. At the same time, the continuous recording allowed the study of the weakening of the interactions with increasing distances. Our purpose was to uncover evidence for allelochemical mechanisms of space occupation and maintenance. A strong non-randomness was found in the interspecific associations. This was mostly due to the interactions of the poecilosclerid sponge Crambe crambe (Schmidt) with its neighbours, especially its negative associations with other sponge species. The strength of the relationships fell drastically over the first few centimeters from the contact borders of the different species. The results pointed strongly to an allelochemical mechanism. The extracts of this sponge featured high bioactivity in laboratory assays, and field experiments demonstrated that the sponge can inhibit the growth of species in the community studied. Standard sampling techniques would have overlooked the spatial structure present in the data. The study emphasizes the need for both contact data and distance data in order to identify the underlying processes reliably. The line transect method provides both types of information easily and allows testing of models and identification of organisms likely to use chemical defenses in space competition. Its use as a preliminary step in studies of chemical ecology might help to detect presumptive allelochemical processes prior to experimental work on the potentially active species.     

Colonization and deterioration processes in Roman mortars by cyanobacteria,algae and lichens

The mortars covering some walls of the Roman city of Baelo Claudia (Cadiz, Spain) support an abundant colonization of cyanobacteria, algae and lichens. The distribution of these organisms is closely related to microclimatic parameters. Furthermore, the development, specific composition and biomass of algal cryptoendolithic communities are related to the wall orientation. The effect of these communities on mortar deterioration is discussed.     

A New Type of Manchette Structure in Spermatids of Culex tigripes(Culicidae)

Abstract In young spermatids of Culex tigripes, microtubules organize a manchette which surrounds the nucleus. When the nucleus elongates, 1–5 expansions appear on the wall of the microtubules. They grow and branch out while the nucleus elongates and chromatin condenses. Expansions are straight or curved in shape. They have the same thickness as the microtubule walls, but they rarely constitute links between microtubules. The manchette disappears naturally at the end of spermiogenesis. The action of colchicine on spermatids leads to the complete disappearance of the microtubules and expansions, and inhibits the lengthening of the nucleus.