Secondary structure prediction of 52 membrane-bound cytochromes P450 shows a strong structural similarity to P450cam

The secondary structure of 52 aligned cytochrome P450 sequences, all of which are membrane bound, is predicted and collectively compared with the crystal structure of the soluble cytochrome P450cam. Ten of 13 helical regions, 6 of 7 beta-pair regions, and beta-structure corresponding to a known beta-bulge near the active site of P450cam are predicted to exist in the membrane-bound P450s. Three turns associated with beta-structure in the soluble enzyme are also predicted for the membrane-bound forms. A strong structural similarity is evident between membrane P450s and the soluble P450cam. Consequently, a multitransmembrane structure involving much of P450 seems highly unlikely. A structure with two N-terminal transmembrane segments is compatible with these observations.     

Distribution of charged residues stabilizes individual helices in myoglobins

The effect of the distribution of charged residues on stability of alpha helices in isolated peptides and in globular proteins exemplified by myoglobins from 62 different species is discussed. A highly simplified set of rules is used to account for the interaction of charged groups with the dipole of an alpha helix. Only the position and sign of a charge with respect to the center of the helix and its ability to participate in intrahelical salt bridges determine its effect. These rules lead to a linear correlation between the helicity in variant C-peptide helices from RNAse and the extent to which the charge distribution opposes the helix dipole. Of the sample of 496 helices in the myoglobins studied, 456 exhibit arrangements of charges which oppose the effective dipole moment of the helix according to this calculation. A number of variants occur which leave the backbone moment of helices A-D unchanged, or even add to it. However no such variants exist in the sequences of helices E-H. We suggest that the E, F, G and H helices in myoglobins which show the strongest reversal of the helix dipole participate in the structures of early intermediates in folding of the chain. Stable helix structures should be more likely to occur in these isolated sequences also, and introduction of charge alterations in helices E to H should affect the initial refolding rate of mutant myoglobins.     

Actual vs perceived profitability: A study of floral choice of honey bees

The relationship between actual and perceived profitability was investigated by quantifying choice behavior of foraging honey bees (Apis mellifera).Rate of net energy gain was used as a measure of profitability. Individual bees repeatedly chose between a yellow and a blue tubular artificial flower which had different associated profitabilities. Handling costs were manipulated by using flowers of different depth;energy gains were manipulated by using different volumes of a 20% (w/w) sucrose solution. Bees' discrimination between the two flowers increased as the absolute difference in profitabilities increased and discrimination decreased as profitabilities of both flowers increased. Therefore, discrimination depended on the relative difference in profitability between flowers, and therefore, perception was a nonlinear function of actual rates of net energy gain. The results also suggested that motivation to choose between flowers depended on the level of profitability. We suggest that nonlinear perceptual scales and motivation should be incorporated into models of food choice as constraints and should be considered in the design of experiments used to test predictions of models and in the interpretation of experimental results.     

Primary Infection of Barley by Erysiphe graminis f. sp. hordei in Relation to Leaf-Age Dependent Resistance and the Roles of the Epidermis and Mesophyll in this Resistance

Abstract The infection frequency of both compatible and incompatible races of Erysiphe graminis f. sp. hordei decreased gradually with increasing leaf age on undetached primary barley leaves. The length of secondary hyphae of the compatible race was approximately the same regardless of age, but secondary hyphae were slightly longer on younger seedlings than on older seedlings in the case of the incompatible race. Both the infection frequency and length of secondary hyphae of the two races weredistinctly different. On composite sections produced by exchanging the epidermal layers of young and relatively mature primary leaves, the infection frequency of the compatible race was higher on the epidermis of young leaves than on the epidermis of older, leaves, regardless of which mesophyll was under the epidermis. The epidermis appears to play a major role in age-dependent resistance, while the mesophyll may act disparately by providing a factor promotive to mildew infection in addition to supporting the resistance function of the epidermis.     

Cell position and light influence C4 versus C3 patterns of photosynthetic gene expression in maize.

C4 plants such as maize partition photosynthetic activities in two morphologically distinct cell types, bundle sheath (BS) and mesophyll (M), which lie as concentric layers around veins. We show that both light and cell position relative to veins influence C4 photosynthetic gene expression. A pattern of gene expression characteristic of C3 plants [ribulose bisphosphate carboxylase (RuBPCase) and light-harvesting chlorophyll a/b binding protein in all photosynthetic cells] is observed in leaf-like organs such as husk leaves, which are sparsely vascularized. This pattern of gene expression reflects direct fixation of CO2 in the C3 photosynthetic pathway, as determined by O2 inhibition assays. Light induces a switch from C3-type to C4-type gene expression patterns in all leaves, primarily in cells that are close to a vein. We propose that light causes repression of RuBPCase expression in M cells, by a mechanism associated with the vascular system, and that this is an essential step in the induction of C4 photosynthesis.     

XY sex reversal syndrome in the mare: clinical and behavioral studies,H-Y phenotype

Summary An inherited genetic disorder causes XY embryos of the horse to develop as mares. On the basis of our study of 38 such mares, we have identified four grades or classes of XY sex reversal according to this scheme: class I, nearly normal female, of which some are fertile; class II, female with gonadal dysgenesis, normal mullerian development; calss III, intersex mare with gonadal dysgenesis, abnormal mullerian development, enlarged clitoris; class IV, virilized intersex characterized by high levels of testosterone. In general, class I and calss II mares were typed H-Y antigen-negative whereas class III and class IV mares were typed H-Y antigen-positive.     

A catalogue of Clostridium thermocellum endoglucanase, β-glucosidase and xylanase genes cloned in Escherichia coli

Abstract Two independent collections of clones containing Clostridium thermocellum genes involved in cellulose have been previously obtained at IAPGR, Cambridge, and at the Pasteur Institute, Paris. The two collections were compared for cross-hybridization, restriction maps and enzyme phenotypes. Truly distinct genes were one β-glucosidase gene, two xylanase genes, and fifteen endogluconase genes. Two of the cloned fragments contained extraneous DNA which was absent from their respective counterparts isolated in the other collection. The dicrepancies resulted from in vivo rearrangements which had occurred in either of the C. thermocellum NCIB 10682 stocks used to generate the two gene banks.     

Trichloroethylene metabolism by microorganisms that degrade aromatic compounds

Trichloroethylene (TCE) was metabolized by the natural microflora of three different environmental water samples when stimulated by the addition of either toluene or phenol. Two different strains of Pseudomonas putida that degrade toluene by a pathway containing a toluene dioxygenase also metabolized TCE. A mutant of one of these strains lacking an active toluene dioxygenase could not degrade TCE, but spontaneous revertants for toluene degradation also regained TCE-degradative ability. The results implicate toluene dioxygenase in TCE metabolism.     

SR Function in malignant hyperthermia

Malignant hyperthermia (MH) is a genetic disease in man and other animal species that predisposes to a catastrophic hypermetabolic syndrome that is triggered by certain anesthetic agents. A working hypothesis is that a defect in regulation of muscle cell calcium is the primary mechanism that initiates the MH syndrome. This paper reviews the evidence for a defect in muscle cell calcium as regulated by the sarcoplasmic reticulum membrane system. Skeletal muscle biopsied from MH man, pigs and dogs has abnormal in vitro contracture response to halothane and caffeine and these responses can be altered by lowering calcium content of the bathing solution and/or the muscle. Measurements of MH muscle cell Ca2+ by Ca2+-specific microelectrodes in vivo and fura-2 in vitro have demonstrated abnormal Ca2+ levels in resting and in caffeine-stimulated states. The SR membrane system is the primary calcium regulating organelle in skeletal muscle and a likely site for the defect in MH muscle. Two Ca2+ regulating functions of the SR have been explored in SR isolated from MH muscle. An abnormality of the 100K Ca2+-ATPase protein that functions to transport Ca2+ from myoplasm to inside the SR does not appear to be responsible for MH. The most probable defective site in the SR appears to be Ca2+ release channels and a Ca2+-induced Ca2+ release pathway has been shown to be abnormal in SR from MH human and pig muscle.