Effects of water activity on reaction rates and equilibrium positions in enzymatic esterifications

A technique of continuous water activity control was used to examine the effects of water activity on enzyme catalysis in organic media. Esterification catalyzed by Rhizopus arrhizus lipase was preferably carried out at a water activity of 0.33, which resulted in both maximal initial reaction rate and a high yield. When Pseudomonas lipase was used as catalyst it was beneficial to start the reaction at high water activity (giving the optimal reaction rate with this enzyme) and then shift to a lower water activity toward the end of the reaction to obtain a high yield. The apparent equilibrium constant of the reaction was influenced by the water activity of the organic solvent. (c) 1994 John Wiley & Sons, Inc.     

Population dynamics of the potato tuber moth on processing tomatoes in Israel

The potato tuber moth (PTM),Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae), is a major pest of processing tomatoes,Lycopersicon esculentum Mill. (Solanaceae), in Israel. The larvae penetrate the tomato fruit through the stem end and present a serious threat to crop quality. Foliage and fruit samples were taken in nine commercial tomato fields located in Israel's three main tomato growing areas, two of which are potato growing areas as well. PTM was not found where potatoes were absent. Potato harvest in nearby fields was found to be the most significant factor affecting seasonal trends in PTM population density in tomatoes. All four larval instars were found in foliage on all sampling dates. Significantly higher proportions of first instars were found during the population density increase which followed potato harvest. Damaged fruits did not contain first instar larvae, indicating that PTM never undergoes complete development within tomato fruit. Fruit damage levels at harvest were positively correlated to the peak mean population densities on foliage and the date they were observed. In tomato fields not adjacent to potatoes, infestation was first observed at the edge of the field. Both before and after the potato harvest in nearby fields, population density at the edge of the field was significantly higher than at the center. In tomato fields adjacent to potatoes, no significant differences were found between population densities at the edge and center before the potatoes were harvested. After the potato harvest, population density at the center of tomato fields was higher than at the edge. Deceased, October 1988     

Some improvements in the quality of NAA procedures and the reliability of the results

After considering the need for quality control in NAA, the concept of quality in NAA procedures themselves is discussed, and some important factors identified. Two approaches to improve quality are then described in more detail. The first concerns the unique ability of NAA using different isotopic reactions and different modes (INAA/RNAA) to provide independent data sets in the same laboratory, thus allowing internal validation or crosschecking. The second discusses the need for chemical yield measurements in RNAA and the advantages of the radioisotopic tracer technique. Some recent advances and further possibilities for this use of tracers are listed.     

Range of photosynthetic control of postillumination P700+ reduction rate in sunflower leaves

The kinetics of the postillumination reduction of P700⁺ which reflects the rate constant for plastoquinol (PQH₂) oxidation was recorded in sunflower leaves at different photon absorption densities (PAD), CO₂ and O₂ concentrations. The P700 oxidation state was calculated from the leaf transmittance at 830 nm logged at 50 s intervals. The P700⁺ dark reduction kinetics were fitted with two exponents with time constants of 6.5 and about 45 ms at atmospheric CO₂ and O₂ concentrations. The time constant of the fast component, which is the major contributor to the linear electron transport rate (ETR), did not change over the range of PADs of 14.5 to 134 nmol cm^-2 s^-1 in 21% O₂, but it increased up to 40 ms under severe limitation of ETR at low O₂ and CO₂. The acceptor side of Photosystem I (PS I) became reduced in correlation with the downregulation of the PQH₂ oxidation rate constant. It is concluded that thylakoid pH-related downregulation of the PQH₂ oxidation rate constant (photosynthetic control) is not present under normal atmospheric conditions but appears under severe limitation of the availability of electron acceptors. The measured range of photosynthetic control fits with the maximum variation of ETR under natural stress in C₃ plants. Increasing the carboxylase/oxygenase specificity would lead to higher reduction of the PS I acceptor side under stress.Abbreviations Cyt b ₆ f cytochrome b ₆ f complex - C_w cell-wall CO₂ concentration, M - ETR electron transport rate - Fd ferredoxin - FNR ferredoxin-NADP reductase - FRL far-red light - PC plastocyanin - PAD photon absorption density nmol cm^-2 s^-1 - PFD photon flux density nmol cm^-2 s^-1 - PS I Photosystem I complex - PQ plastoquinon - PQH₂ plastoquinol - PS II Photosystem II complex - P700 Photosystem I donor pigment, reduced - S830 830 nm signal (D830, difference of S830 from the dark level) - WL white light - Y_l maximum quantum yield of PS I electron transport, rel. un     

Regulation of replication of plasmid pBR322 in amino acid-starved Escherichia coli strains

The stringent response causes inhibition of replication of plasmid pBR322 in amino acid-starved Escherichia coli cells whereas in relaxed mutants the replication of this plasmid proceeds for several hours. On the basis of density shift experiments and pulse-labelling experiments we showed that most of the pBR322 molecules begin replication during the relaxed response and the rate of plasmid DNA synthesis in unstarved and isoleucine-starved relA ^–] bacteria is similar. We found that the Rom function plays a key role in the stringent control of plasmid pBR322 replication, as insertional inactivation of the rom gene causes amplification of pBR322rom ^– in both relA ^– and relA ⁺ strains during amino acid starvation. Moreover, pUC19, which is a pBR322-derived plasmid lacking the rom gene, behaves like pBR322rom ^–, whereas introduction of the rom gene into the pUC19 replicon drives it into the pBR322 mode of replication in amino acid-starved bacteria. A model for the regulation of pBR322 plasmid DNA replication by Rom protein in amino acid-starved Escherichia coli strains is proposed.     

Preliminary caged‐field trial,using the fungal pathogen Zoophthora radicans brefeld (zygomycetes: entomophthorales) against the diamondback moth Plutella xylostella L. (lepidoptera: Yponomeutidae) in the UK

Zoophthora radicans Brefeld was tested for control of Plutella xylostella L. in a caged‐field trial. No infection was seen in control cages, but between 36% and 68% of larvae in live samples, and 38% and 55% of larvae at the final harvest, were infected in inoculated cages, suggesting the biological control potential of this fungus.     

Mitochondrial DNA control region polymorphisms: genetic markers for ecological studies of marine turtles

We describe a rapid and sensitive method for the detection of population-specific genetic markers in mitochondrial DNA (mtDNA) and the use of such markers to analyse population structure of marine turtles. A series of oligonucleotide primers specific for the amplification of the mtDNA control region in Cheloniid turtles were designed from preliminary sequence data. Using two of these primers, a 384–385-bp sequence was amplified from the 5′ portion of the mtDNA control region of 15 green turtles Chelonia mydas from 12 different Indo-Pacific rookeries. Fourteen of the 15 individuals, including some with identical whole-genome restriction fragment patterns, had sequences that differed by one or more base substitutions. Analysis of sequence variation among individuals identified a total of 41 nucleotide substitutions and a 1-bp insertion/deletion. Comparison with evidence from whole-genome restriction enzyme analysis of the same individuals indicated that this portion of the control region is evolving approximately eight times faster than the average rate and that the sequence analysis detected approximately one fifth of the total variation present in the genome. Restriction enzyme analysis of amplified products from an additional 256 individuals revealed significant geographic structuring in the distribution of mtDNA genotypes among five of the 10 rookeries surveyed extensively. Additional geographic structuring of genotypes was identified through denaturing gradient gel electrophoresis (DGGE) of amplified products. Only two of the 10 rookeries surveyed could not be differentiated, indicating that the Indo-Pacific C. mydas include a number of genetically differentiated populations, with minimal female-mediated gene flow among them. Important applications for genetic markers in the conservation and management of marine turtles include the identification of appropriate demographic units for research and management (i.e. genetically discrete populations) and assessment of the composition of feeding and harvested populations.     

厌氧消化过程的非模型控制

对废水淤泥的厌氧消化处理过程进行了研究．提出了一种基于神经网络的非模型控制方法。多变量控制系统的操作变量为供热量和进水量．被控变量为消化温度和消化污泥排出浓度。证明了控制算法的收敛性。讨论了控制系统的稳定性。仿真结果证实了非模型控制方法的有效性。该方法无需对象的模型．为复杂生化过程的控制提供了一种新途径。     

Flight-correlated activity changes in neurons of the lateral accessory lobes in the brain of the locust Schistocerca gregaria

The study investigates activity changes in neurons of the lateral accessory lobes in the brain of the locust Schistocerca gregaria during wind-elicited tethered flight. Neurons with ascending projections from the ventral nerve cord to the lateral accessory lobes showed flight-associated excitations which were modulated in the flight motor rhythm. Descending neurons with ramifications in the lateral accessory lobes were tonically excited corresponding to flight duration. The onset of wind-elicited responses in the descending neurons preceded the onset of flight motor activity by 22–60 milliseconds. Neurons connecting the lateral accessory lobes with the central body, the anterior optic tubercles, or other brain areas showed a variety of responses including activity changes during flight initiation and flight termination. Activity in many of these neurons was less tightly coupled to the flight situation and often returned to background levels before flight was terminated. Most of the recorded neurons responded, in addition, to stationary visual stimuli. The results suggest that the lateral accessory lobes in the locust brain are integrative links between the central body, visual pathways, and the ventral nerve cord. The possible involvement of these brain areas in flight control is discussed.     

Gain control in a proprioceptive feedback loop as a prerequisite for working close to instability

In the artificially closed femur-tibia control system of stick insects oscillations were induced in 3 different ways: Increasing the phase-shift by introducing an electronic delay, afference sign reversal and coupling the tibia to an inert mass. In all 3 cases the oscillations stopped after some time. The gain of the open-loop system was significantly smaller after the oscillations. Afference sign reversal by surgically crossing of the receptor apodeme of the femoral chordotonal organ for 25–85 days does not lead to altered characteristics of the control loop. When sinusoidal passive movements are forced upon the intact femur-tibia joint the forces resisting these movements do not decrease with time. In contrast to direct stimulation of the femoral chordotonal organ, these passive movements also influence the contralateral leg. The experiments show that the gain-control system of the femur-tibia control loop of stick insects consists of at least two components: A sensitization system (with inputs from many kinds of stimuli indicating some kind of disturbance) increases the gain of all reflex loops. A specific habituation-like system decreases the gain with repetitive stimulation only of one control system.Abbreviations fCO femoral chordotonal organ - SETi slow extensor tibiae motor neuron