Mechanical design of polypterid fish integument for energy storage during recoil aspiration

Polypterid fishes ventilate their lungs by recoil aspiration. Active exhalation compresses the bony scale jacket; inhalation occurs when the scale jacket recoils to its original shape. Exhalation and loading of the integument are powered by contraction of striated muscle in the lung walls. The integument of polypterid fishes consists of interlocking rhomboid scales held together by collagen fibre strands. The scales imbricate with bevelled edges, so that when the fish is at rest, its integument is circular in cross-section and the overlapping scale edges are parallel. During exhalation, the hemicircular shape of the ventral integument is deformed, and the scales rotate slightly. As the overlapping scale edges become non parallel, the scales act as tiny levers to stretch the collagen fibres between them. When the fish opens its glottis to inhale, the stretched collagen fibres return to their rest lengths and pull the scale jacket back into a circular shape, sucking air into the lungs. Thus, despite the deformation of the integument as a whole in compression, strain energy is stored in tensile elements.     

Biocide application for increasing storage periods and maintaining quality and chemical constituents of banana fruits

Banana fruits were treated with biocides formulated from essential oils of anise, coriander or black cumin seeds. Treated and non-treated fruits were stored at temperatures of 5, 10, 15 and 20°C. Samples were stored for periods of 10, 20, 30, 40, 50 and 60 days. The collected samples in each interval were subjected to estimation of decay development and quality degree, in addition to the chemical constituents of starch, sugars, vitamin C of pulp and peel chlorophyll content. Results reveal that non-treated banana fruits decayed continuously by lapse of storage periods. However, this decay was significantly delayed by lowering the storage temperature. Soaking banana fruits in the tested biocides showed a positive potential for interrupting the decay in stored banana fruits and this promising impact was much more pronounced at lower storage temperature. Further, biocide treated banana fruits kept their good quality for longer storage periods compared to non-treated fruits, due to lower ripening rates which promisingly prolonged shelf-life. As the starch content gradually decreased during storage, the total sugar content increased. On the other hand, biocide application retarded the conversion of starch into simple sugars, especially at the low temperature rate. Additionally, the imposed treatments maintained vitamin C in banana pulp and lowered the decline in peel chlorophyll content.     

Kinetics of coupled enzyme reactions

A theory has been developed for the kinetics of coupled enzyme reactions. This theory does not assume that the first reaction is irreversible. The validity of this theory is confirmed by a model system consisting of enoyl-CoA hydratase (EC 4.2.1.17) and 3-hydroxyacyl-CoA dehydrogenase (EC 1.1.1.35) with 2,4-decadienoyl coenzyme A (CoA) as a substrate. This theory, in contrast to the conventional theory, proves to be indispensible for dealing with coupled enzyme systems where the equilibrium constant of the first reaction is small and/or the concentration of the coupling enzyme is higher than that of the intermediate. Equations derived on the basis of this theory can be used to calculate steady-state velocities of coupled enzyme reactions and to predict the time course of coupled enzyme reactions during the pre steady state.     

Bovine serum eliminates rapid nonspecific toxic reactions during bioassay of stored fish for Clostridium botulinum toxin

When stored fish or some fish products were tested for the presence of Clostridium botulinum toxin, nonspecific toxic reactions in mice often occurred, rendering the bioassay inconclusive. The nonspecific toxic reactions were mediated by the gram-negative microbiota, inherent to the fish, which were the source of lethal, heat-stable endotoxins. The treatment of assay samples with bovine serum eliminated nonspecific reactions through the interaction of constituent serum immunoglobulin M (IgM) with endotoxic material. Removal of IgM from bovine serum through treatment with protein A or concanavalin A resulted in a loss of protective activity.     

Effect of organic selenium on turkey semen quality during liquid storage

The aim of the present study was to evaluate the effect of dietary organic selenium on the turkey semen during storage. Twenty males (BUT, Big 6, 40 weeks of age) were divided into control (n = 10) and experimental group (n = 10). The turkeys in the both groups were fed with a commercial diet containing 0.1 ppm Se in the form of sodium selenite. The experimental birds were additionally supplied with 0.3 ppm organic Se in the form Sel-Plex™ (Alltech, Inc.). After 30 days of feeding, the semen samples were collected twice a week for the 3 weeks of the study and diluted 1 + 1 (v/v) with TUR-2 diluent, and stored in a water bath (+10 to 15° C) for 6 h. The percentage of motile spermatozoa, the sperm viability (live/dead spermatozoa), total lipids, phospholipids and total cholesterol were assessed in fresh and stored semen. The fertilizing ability of semen was assessed by artificial insemination of 30 hens per group with dose containing 200 × 10⁶ spermatozoa weekly. After 6 h of semen storage, the motility of spermatozoa decreased significantly in the control group (by 8.7 relative percent, P < 0.05) and only by four relative percent (P > 0.05) in experimental group reflecting a protective effect of dietary Se supplementation. The proportion of live spermatozoa was higher in fresh semen and significantly lower in stored semen. The positive effect of Se supplementation was observed on the lipid composition of stored semen: the concentration of the total lipids and phospholipids in the seminal plasma from control group significantly increased, while in the experimental group remained constant. Better semen integrity in the experimental group was associated with an improved fertilizing ability of spermatozoa: the fertility rate of stored spermatozoa in the control group was 88%, while in the experimental group was 90.5%.     

Effect of dialysis on quality characteristics of turkey semen during liquid storage

Low molecular weight substances such as zinc and peroxides are present in seminal plasma and are responsible for deleterious effects in stored semen. On the contrary, molecules larger than 50 kDa are beneficial to in-vitro storage of spermatozoa. Since the effects of different seminal plasma fractions in turkey semen are not completely known, the purpose of the study was to determine the effects of turkey semen dialysis with a 12-14 kDa cut-off on viability, hypo-osmotic membrane integrity, or sperm motility of turkey spermatozoa stored up to 48 h at 5 degrees C. Twelve pools of semen, each pool originating from four toms, were used. Each pool was divided into two aliquots, one of which was dialyzed while the other represented the control. Each semen aliquot was evaluated for sperm viability, membrane integrity and motility after 6, 24 and 48 h of in-vitro storage. Cold storage of turkey semen for 48 h significantly worsened (P<0.01) sperm viability, hypo-osmotic membrane integrity, and sperm motility index of both control and dialyzed samples. After 24 and 48 h sperm viability, membrane integrity and sperm motility index were better (P<0.01) in dialyzed semen compared to the control.     

On the chemical reactions for chemotaxis in bacteria

Chemical reactions in bacterial chemoreceptors are considered. It is shown that the model proposed by Macnab and Koshland explains the experimental facts not completely. Two modifications of the Macnab-Koshland's model are proposed in which the co-operative feedback control plays an important role.     

Pyrimidine-specific chemical reactions useful for DNA sequencing.

Potassium permanganate reacts selectively with thymidine residues in DNA (1) while hydroxylamine hydrochloride at pH 6 specifically attacks cytosine (2). We have adopted these reactions for use with the chemical sequencing method developed by Maxam and Gilbert (3).     

Investigation of a Monte Carlo model for chemical reactions

Monte Carlo computer simulations are in use at a number of laboratories for calculating time-dependent yields, which can be compared with experiments in the radiolysis of water. We report here on calculations to investigate the validity and consistency of the procedures used for simulating chemical reactions in our code, RADLYS. Model calculations were performed of the rate constants themselves. The rates thus determined showed an expected rapid decline over the first few hundred ps and a very gradual decline thereafter out to the termination of the calculations at 4.5 ns. Results are reported for different initial concentrations and numbers of reactive species. Generally, the calculated rate constants are smallest when the initial concentrations of the reactants are largest. It is found that inhomogeneities that quickly develop in the initial random spatial distribution of reactants persist in time as a result of subsequent chemical reactions, and thus conditions may poorly approximate those assumed from diffusion theory. We also investigated the reaction of a single species of one type placed among a large number of randomly distributed species of another type with which it could react. The distribution of survival times of the single species was calculated by using three different combinations of the diffusion constants for the two species, as is sometimes discussed in diffusion theory. The three methods gave virtually identical results. Received: 6 May 1998 / Accepted in revised form: 5 July 1998     

Kinetics of primer-dependent polynucleotide phosphorylase synthetic reactions

The kinetics of a model for the primer-dependent, polynucleotide phosphorylase-catalyzed synthesis of oligo- and polynucleotides is developed. Numerical solutions are presented which correspond to a wide variety of possible reaction conditions. The model seems capable of explaining the types of behavior which have been experimentally observed for polynucleotide phosphorylase reactions. The most unusual of these is the presence of a transient intermediate of high molecular weight polynucleotide chains which is subsequently degraded to an equilibrium mixture of short oligonucleotides. Methods of estimating the time of occurrence and maximum size of the polymer are discussed. Analytical solutions are developed for the concentrations of free enzyme and unreacted nucleoside diphosphate. In conjunction with equilibrium data these may permit the rate constants required by the model to be determined.     

Secondary structure prediction of seed storage proteins

The comparison of partial primary structure of seed storage proteins leads to show homologies inside of each considered family (Legume seed legumins and cereal prolamins). Predicted secondary structures deduced from the presently known sequences also exhibit considerable homologies, which implies a severe conservatism of these proteins. Short repetitive segments of sequence of 5-20 residues are frequently occurring and give rise to the prediction either of beta-structure (or alpha-helix) bonded by beta-turns or of successive beta-turns. The latter conformation, which would be able to form a helicoidal arrangement, could contribute to a maximal packing of the protein molecules inside of the subcellular organelles (protein bodies) within which they are confined. As the only known function of seed storage proteins is to provide amino acids to the embryo, it is suggested that their ability to occupy a minimal volume is actually a reasonable explanation of their extreme conservatism in the course of evolution.     

Kinetics of lysosomal storage of indigestible matter.

In lysosomal storage diseases and in accumulation of lipofusion in the lysosomes there is a gradual eroding of the lysosomal system due to overloading the lysosomes by molecules which cannot be digested or expelled. The kinetics of this accumulation is examined for tissue cultures in terms of the cell growth rate, lysosomal production rate, and of generation of the indigestible element.