Enzymatic reaction kinetic: comparison in an organic solvent and in supercritical carbon dioxide

Myristic acid esterification has been performed by an immobilized lipase from Mucor Miehei both in n-hexane and in supercritical carbon dioxide (SCCO(2)). The enzyme is stable in SCCO(2) at 15 MPa and 323 K. The reaction rate is influenced by the concentration of water and by the reaction medium composition. A reaction mechanism is proposed, and kinetic parameters are determined at 12.5 MPa and 313 K. Maxium velocity appears 1.5-fold higher in SCCO(2) than in n-hexane; however, as solubility of myristic acid is greater in n-hexane, it is not yet definitively clear that the supercritical medium is more favorable than the classical organic solvent for this type of enzyme reaction.     

Injection of cells and monoclonal antibodies into mice: comparison of tail vein and retroorbital routes

Organ distribution and blood concentration profiles were compared following injection of mice with radiolabeled test agents via the lateral tail vein or retroorbital venous sinus. Monoclonal antibodies directed against B16 melanoma of C57BL/6 origin were labeled with iodine-125. Thymocytes from BALB/c mice and B16 melanoma cells were labeled with technetium-99m sodium pertechnetate (Na 99mTcO4). Animals were injected with 5 microCI of iodinated antibody, 5 X 10(5) syngeneic thymocytes, 2.5 X 10(5) melanoma cells, or 10 microCi Na 99mTcO4 in 0.2 ml saline via either route. In non-tumor-bearing C57BL/6 mice radiolabeled monoclonal antibody was found primarily in the gastrointestinal tract, liver, and blood. Na 99mTcO4 localized in the gastrointestinal tract, 99mTc-labeled thymocytes in the spleen and liver, and 99mTc-labeled B16 melanoma cells in the liver and lungs. Pharmacokinetic analysis of blood samples taken 4, 8, and 12 min following injection of the labeled agents suggested that the iodinated antibody had less vascular permeability than Na 99mTcO4 and that thymocytes and B16 melanoma cells were trapped in the pulmonary vasculature as they passed through the lungs. It is noteworthy that no biologically significant differences in organ distribution patterns or blood decay profiles were found between lateral tail vein and retroorbital routes. The data clearly indicate that these routes can be used interchangeably with one another for intravenous injections.     

Mechanism of proline-specific proteinases: (I) Substrate specificity of dipeptidyl peptidase IV from pig kidney and proline-specific endopeptidase from Flavobacterium meningosepticum

The substrate specificity of dipeptidyl peptidase IV (dipeptidyl peptide hydrolase, EC 3.4.14.5) from pig kidney and proline-specific endopeptidase from Flavobacterium meningosepticum, was investigated with a series of N-terminal unprotected (dipeptidyl peptidases IV) and succinylated dipeptidyl-p-nitroanilides (proline-specific endopeptidase). Both enzymes are specific for the S configuration of the amino-acid residue in P1 and P2 position if the penultimate residue is proline. In the case of alanine substrates (Ala in P1, dipeptidyl peptidase IV hydrolyzes such compounds where the configuration of the P2 residue is R. The penultimate residue with dipeptidyl peptidase IV can be, beside proline and alanine, dehydroproline, hydroxyproline and pipecolic acid. Proline substrates (Pro in P1) with an R configuration in P2 are inhibitors of the hydrolysis of proline substrates with an S,S configuration in an uncompetitive (dipeptidyl peptide IV) or mixed inhibition type (proline-specific endopeptidase). Derivatives of Gly-Pro-pNA where the N-terminal amino group is methylated are hydrolyzed by dipeptidyl peptidase IV.     

Model studies on the mechanical significance of grouping in compound spider slit sensilla (Chelicerata,Araneida)

Summary The mechanical implications of various types of slit arrangements found among the strain-sensitive slit sensilla in the arachnid exoskeleton (Fig. 3) were studied by measuring the deformation of model slits, cut into plastic discs, under static load applied in the plane of the disc and from varying directions (Figs. 1, 2).1. Close parallel, lyriform arrangements. Compression of slits (adequate stimulus) reaches much higher values than dilatation. It is highest with the load direction at right angle to the slit axes. Also, in the majority of slits the range of load angles resulting in compression is considerably larger than that leading to dilatation. Length distribution and lateral shift of slits in the models have a pronounced effect on slit deformability (Figs. 4-5): (a) In the oblique bar arrangement with slits of equal length and regular lateral shift (Fig. 4A) deformation of all slits is very similar at all load directions. In all slits compression results from a range of load angles larger than 120°. (b) In arrangements with a regular increase in slit length and a triangular outline shape deformability differs greatly among the slits at all load angles (Fig. 4B). (c) The slit configuration with a heartshaped outline (Fig. 4C) is peculiar for the large spread of load angles at which the compression of the different slits is highest. — These properties recommend different arrangements for the solution of different strain measuring problems, with for instance, the particular need of a wide angular working range (arrangement a), of a large spectrum of absolute sensitivities (b), or of the analysis of load direction (c).2. Angle and distance between slits. Due to the mechanical directionality inherent in an elongated slit the divergence of slit axes within a group of slits is likely to indicate the importance of the analysis of strain direction (Fig. 6). The mechanical interaction between closely neighbouring slits decreases with their distance from each other. In a parallel arrangement of equally long slits it disappears if the distance is about 1.5 times the slit length (Fig. 7).3. Aiming towards a mechanical model which would explain the complex deformation found in a lyriform organ, we consider the outline of the organ as a hole traversed by beams of material. Slit deformation can be calculated from the elastic lines of the beams which separate the slits and information drawn from photoelastic experiments (Figs. 8-11).     

Purification of a neutral proteinase, associated with the actomyosin complex, from uterine myometrium.

We have purified and characterized a neutral proteinase activity from pig uterine myometrium. The proteinase co-purified with the actomyosin complex and could only be separated from it by a high concentration of a chaotropic ion, 3M-NaBr. The proteinase was further purified by gel filtration and affinity chromatography. The purified protein showed a single band on sodium dodecyl sulphate/polyacrylamide-gel electrophoresis corresponding to an Mr of 28 000. Gel filtration on Sephadex G-100 in a buffer containing 3M-NaBr gave an Mr of 27 500. Without the addition of the chaotropic Br- ion, the proteinase aggregates to high-Mr forms of more than 10(6)Da. The proteinase has optimum hydrolytic activity with casein as substrate at pH 7.5-8.0. The thiol-group-blocking reagents p-chloromercuribenzoate, p-chloromercuribenzenesulphonate and Hg2+, as well as soya-bean trypsin inhibitor and 4-aminobenzamidine, inhibited the proteinase. Other bivalent cations, chelating agents and the serine-specific reagents 7-amino-1-chloro-3-tosylamido-L-heptan-2-one and phenylmethanesulphonyl fluoride were without any effect on proteinase activity. The proteinase degraded myosin very rapidly at a molar ratio of proteinase to myosin of 1:50, concomitant with the rate of loss of the ATPase activity. Compared with myosin, actin was only a poor substrate and was degraded at a much lower rate, even at a high molar ratio of the proteinase to actin.     

Human neutrophil interactions of a bispecific monoclonal antibody targeting tumor and human Fcγ RIII

 2B1 is a bispecific murine monoclonal antibody (bsmAb) targeting the c-erbB-2 and CD16 (FcγRIII) antigens. c-erbB-2 is over-expressed by a variety of adenocarcinomas, and CD16, the low-affinity Fcγ receptor for aggregated immunoglobulins, is expressed by polymorphonuclear leukocytes (PMN), natural killer (NK) cells and differentiated mononuclear phagocytes. 2B1 potentiates the in vitro lysis of c-erbB-2 over-expressing tumors by NK cells and macrophages. In this report, the interactions between 2B1 and PMN were investigated to assess the impact of these associations on in vitro 2B1-promoted tumor cytotoxicity by human NK cells. The peak binding of 2B1 to PMN was observed at a concentration of 10 μg/ml 2B1. However, 2B1 rapidly dissociated from PMN in vitro at 37°C in non-equilibrium conditions. This dissociation was not caused by CD16 shedding. When PMN were labeled with ¹²⁵I-2B1 and incubated at 37°C and the supernatants examined by HPLC analysis, the Fab regions of dissociated 2B1 were not complexed with shed CD16 extracellular domain. While most of the binding of 2B1 to PMN was solely attributable to Fab-directed binding to FcγRIII, PMN-associated 2B1 also bound through Fcγ-domain/FcγRII interactions. 2B1 did not promote in vitro PMN cytotoxicity against c-erbB-2-expressing SK-OV-3 tumor cells. When PMN were coincubated with peripheral blood lymphocytes, SK-OV-3 tumor and 2B1, the concentration of 2B1 required for maximal tumor lysis was lowered. Although PMN may serve as a significant competitive binding pool of systemically administered 2B1 in vivo, the therapeutic potential of the targeted cytotoxicity properties of this bsmAb should not be compromised. Received: 3 May 1995 / Accepted: 6 February 1996     

Long-term effects of ungulates on phytophagous insects

Abstract.  1. Most plants interact with a diverse suite of herbivores, allowing the opportunity for the existence of positive and negative interactions between highly dissimilar organisms. However, most studies on herbivorous interactions have been performed under the assumption that they occur mainly between similar species. Consequently, ecologists are still far from a full understanding of the ecological factors that determine insect population dynamics.
2. In this study, a 7-year field experiment was conducted that manipulated the presence of ungulates to evaluate their effects on the abundance, attack rate, and survival of four guilds of co-occurring herbivorous insects living on the same host plant: seed predators, stem borers, gall makers and sap suckers. These four guilds differed in habits and behaviour, the first three being sessile and endophytic and the last being free-living.
3. This study shows that the abundance of all four guilds was negatively affected by ungulates. However, the effect on attack rate differed among guilds, as mammals do not affect the seed predator attack rate. Ungulates also differentially affected insect survival, ingesting only seed predators and gall makers.
4. In summary, this study suggests that diverse mechanisms may affect different insect guilds in different ways. Therefore, competition between disparate herbivores appears to be complex and can be provoked by multiple mechanisms.     

Indentation as a technique to assess the mechanical properties of fallback foods

A number of living primates feed part-year on seemingly hard food objects as a fallback. We ask here how hardness can be quantified and how this can help understand primate feeding ecology. We report a simple indentation methodology for quantifying hardness, elastic modulus, and toughness in the sense that materials scientists would define them. Suggested categories of fallback foods—nuts, seeds, and root vegetables—were tested, with accuracy checked on standard materials with known properties by the same means. Results were generally consistent, but the moduli of root vegetables were overestimated here. All these properties are important components of what fieldworkers mean by hardness and help understand how food properties influence primate behavior. Hardness sensu stricto determines whether foods leave permanent marks on tooth tissues when they are bitten on. The force at which a food plastically deforms can be estimated from hardness and modulus. When fallback foods are bilayered, consisting of a nutritious core protected by a hard outer coat, it is possible to predict their failure force from the toughness and modulus of the outer coat, and the modulus of the enclosed core. These forces can be high and bite forces may be maximized in fallback food consumption. Expanding the context, the same equation for the failure force for a bilayered solid can be applied to teeth. This analysis predicts that blunt cusps and thick enamel will indeed help to sustain the integrity of teeth against contacts with these foods up to high loads. Am J Phys Anthropol 140:643–652, 2009. © 2009 Wiley-Liss, Inc.     

The importance of fallback foods in primate ecology and evolution

The role of fallback foods in shaping primate ranging, socioecology, and morphology has recently become a topic of particular interest to biological anthropologists. Although the use of fallback resources has been noted in the ecological and primatological literature for a number of decades, few attempts have been made to define fallback foods or to explore the utility of this concept for primate evolutionary biologists and ecologists. As a preface to this special issue of the American Journal of Physical Anthropology devoted to the topic of fallback foods in primate ecology and evolution, we discuss the development and use of the fallback concept and highlight its importance in primatology and paleoanthropology. AmJ Phys Anthropol 140:599–602, 2009. © 2009 Wiley-Liss, Inc.