Design and mechanical properties of insect cuticle

Since nearly all adult insects fly, the cuticle has to provide a very efficient and lightweight skeleton. Information is available about the mechanical properties of cuticle-Young's modulus of resilin is about 1 MPa, of soft cuticles about 1 kPa to 50 MPa, of sclerotised cuticles 1-20 GPa; Vicker's Hardness of sclerotised cuticle ranges between 25 and 80 kgf mm(-2); density is 1-1.3 kg m(-3)-and one of its components, chitin nanofibres, the Young's modulus of which is more than 150 GPa. Experiments based on fracture mechanics have not been performed although the layered structure probably provides some toughening. The structural performance of wings and legs has been measured, but our understanding of the importance of buckling is lacking: it can stiffen the structure (by elastic postbuckling in wings, for example) or be a failure mode. We know nothing of fatigue properties (yet, for instance, the insect wing must undergo millions of cycles, flexing or buckling on each cycle). The remarkable mechanical performance and efficiency of cuticle can be analysed and compared with those of other materials using material property charts and material indices. Presented in this paper are four: Young's modulus-density (stiffness per unit weight), specific Young's modulus-specific strength (elastic hinges, elastic energy storage per unit weight), toughness-Young's modulus (fracture resistance under various loading conditions), and hardness (wear resistance). In conjunction with a structural analysis of cuticle these charts help to understand the relevance of microstructure (fibre orientation effects in tendons, joints and sense organs, for example) and shape (including surface structure) of this fibrous composite for a given function. With modern techniques for analysis of structure and material, and emphasis on nanocomposites and self-assembly, insect cuticle should be the archetype for composites at all levels of scale.     

Chloridazon-catechol dioxygenases, a distinct group of meta-cleaving enzymes

We previously described a new meta-cleaving enzyme, termed chloridazon-catechol dioxygenase. The present paper describes the comparison of this enzyme with the meta-cleaving enzymes of eighteen strains of soil bacteria isolated with various aromatic compounds. Four of these strains were isolated with the herbicide chloridazon, six with the analgeticum aminopyrine and one with the analgeticum antipyrine as sole carbon source. These strains all belonged to a new type of bacteria, called Phenylobacteria. The seven other strains were isolated with aromatic compounds such as toluene, 3-phenylpropionate, benzoate, papaverine and 4-chlorobenzoate, and belonged to various species including Pseudomonas, Acinetobacter and Nocardia. In double diffusion experiments with antibodies, prepared against chloridazon-catechol dioxygenase, extracts from the eleven strains of Phenylobacteria gave a cross reaction, whereas the extracts of the seven other strains showed no reaction. The enzymes of the eleven positive strains showed the same characteristic kinetic behaviour as the previously described enzyme. In contrast to catechol 2, 3-dioxygenase they needed the addition of exogenous Fe2+ ions for activity. On ion-exchange chromatography they emerged at the same buffer concentration as chloridazon-catechol dioxygenase. In polyacrylamide electrophoresis they migrated identically. The linkage map derived from the activities of the various enzymes with 10 different substrates revealed an identity of more than 80% for these eleven enzymes. So the meta-cleaving enzymes of the Phenylobacteria seem to form a distinct group among the non-heme iron-containing dioxygenases.     

Wood for sound

The unique mechanical and acoustical properties of wood and its aesthetic appeal still make it the material of choice for musical instruments and the interior of concert halls. Worldwide, several hundred wood species are available for making wind, string, or percussion instruments. Over generations, first by trial and error and more recently by scientific approach, the most appropriate species were found for each instrument and application. Using material property charts on which acoustic properties such as the speed of sound, the characteristic impedance, the sound radiation coefficient, and the loss coefficient are plotted against one another for woods. We analyze and explain why spruce is the preferred choice for soundboards, why tropical species are favored for xylophone bars and woodwind instruments, why violinists still prefer pernambuco over other species as a bow material, and why hornbeam and birch are used in piano actions.     

Immunoreactivity of gastric ECL and A-like cells in fasted and fed rats and mice

The oxyntic mucosa of rat and mouse stomach harbors histamine-producing ECL cells and ghrelin-producing A-like cells. The ECL cells are known to be active when the circulating gastrin levels are elevated in response to food intake. The A-like cells are the main source of circulating ghrelin. In response to starvation, the circulating ghrelin is elevated as a hunger signal. The aim of the present work was to study the correlation between the immunoreactivities and cellular activities of the ECL cells and A-like cells. Rats were either fed or fasted for 48 h and mice for 24 h. Immunohistochemical examination with antiserum against chromogranin A-derived fragment pancreastatin revealed both the ECL cells and the A-like cells without a difference between fasted and fed animals. Histamine was limited to the ECL cells with no significant difference between fasted and fed animals. Histidine decarboxylase (HDC) immunoreactivity occurred predominately in the ECL cells of the fed, but not fasted, animals in which the HDC enzymatic activity in the oxyntic mucosa was higher than in fasted animals. Ghrelin immunoreactivity was increased in terms of intensity, but not cell density in fasted animals. Thus, the immunoreactivities of ECL cells and A-like cells might be affected by starvation.