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911.
The synthetic peptide pilosulin 1, corresponding to the largest defined allergenic polypeptide found in the venom of the jumper ant Myrmecia pilosula, inhibited the incorporation of [methyl-3H]thymidine into proliferating Epstein–Barr transformed (EBV) B-cells. The LD50 was four-fold lower in concentration than melittin, a cytotoxic peptide found in honey bee venom. Loss of cell viability was assessed by flow cytometry by measuring the proportion of cells that fluoresced in the presence of the fluorescent dye 7-aminoactinomycin D. Examination of proliferating EBV B-cells indicated that the cells lost viability within a few minutes exposure to pilosulin 1. Partial peptides of pilosulin 1 were less efficient in causing loss of cell viability and the results suggest that the 22 N-terminal residues are critical to the cytotoxic activity of pilosulin 1. Normal blood white cells were also labile to pilosulin 1. T- and B-lymphocytes, monocytes and natural killer cells, however, were more labile than granulocytes. Analysis of pilosulin 1 using circular dichroism indicated that, in common with melittin and other Hymenoptera venom toxins, it had the potential to adopt an α-helical secondary structure.  相似文献   
912.
913.
The preparation of monoclonal antibodies raised against antigens of salivary gland extracts of femaleRhipicephalus evertsi evertsi is reported. Nine hybridoma cell lines were established of which eight secreted IgG3 and one IgG1. The immune response was biased towards immunogens unique to the prefed stage of the tick salivary glands by prior cyclophosphamide suppression of the immune response against unfed tick salivary glands. Immunoblots of salivary gland antigens, separated by SDS-PAGE showed reactivity with three of the monoclonal antibodies, all of which had identical specificity for antigens unique to prefed salivary extracts. Each of these monoclonal antibodies identified two prominent bands with relative molecular masses corresponding to 23 and 46 and a third minor band with molecular mass of 70 kDa.  相似文献   
914.
Cystathionine gamma-synthetase (EC 4.2.99.9), a key enzyme in bacterial methionoine biosynthesis, has been found to use L-vinylglycine (2-amino-3-butenoate) and L-beta-haloaminobutyrates (X = F, Cl) as substrates in addition to the physiological gamma-substituted substrate O-succinyl-L-homoserine (OSHS). Vinylglycine is a substrate both for alpha-ketobutyrate formation (the normal product from gamma elimination with OSHS) and for cystathionine formation (the normal gamma-replacement product with OSHS) in the presence of cysteine. This behavior substantiates that the stabilized vinylglycine--pyridoxal phosphate (PLP) alpha carbanion is the key partitioning species in this enzyme's catalysis. The Vmax values for ketobutyrate production and cystathonine formation from vinylglycine are equivalent at approximately 45 U/mg, whereas the corresponding Vmax values from OSHS are 20 and 200 U/mg, respectively, suggesting different rate-determining steps with these two substrates. The beta-haloaminobutyrates undergo catalyzed HX elimination to yield bound aminocrotonate--PLP directly as a an initial intermediate and as a precursor of ketobutyrate. Little or no cystathionine formation is detectable when these substrates are incubated with enzyme and the normal cosubstrate cysteine, strongly indicating that the aminocrotonate--PLP intermediate is not in rapid, reversible equilibrium with the stabilized vinylglycine--PLP carbanion; in normal catalysis, the prototropic shift from alpha carbanion to aminocrotonate appears functionally unidirectional. The HX-elimination step from beta-chloroaminobutyrate is nonconcerted as demonstrated by a 3H2O in equilibrium chloroaminobutyrate exchange reaction. Further suggestion for discrete beta-halo-alpha-carbanionic intermediates derives from the observation that the haloaminobutyrates appear to a partition between ketobutyrate formation and enzyme inactivation. Since neither vinylglycine nor OSHS causes any detectable inactivation during turnover, it is likely that the inactivation species is not a common intermediate, i.e., the electrophilic aminocrotonate--PLP species (a potential Michael acceptor), but rather a species peculiar to the beta-haloaminobutyrate pathway. The beta-halo-alpha-carbanion--PLP intermediate has beta-halo-alpha-iminodihydropyridine character in the p-quinoid resonance contributor and is a good candidate for an alkylating agent by an SN2--displacement mechanism. Spectroscopic analyses of incubations with the various amino acid substrates show a number of long-wavelength absorbing species forming during turnover, tentative assignments are suggested.  相似文献   
915.
916.
Abstract

The large holasteroid echinoid Hemipneustes striatoradiatus (Leske) was exploited by diverse invertebrate encrusters and borers during the Maastrichtian, both pre- and post-mortem. In life, the specimen described herein was perforated by multiple Oichnus simplex Bromley borings close to the apical system. Each engendered a growth reaction from the echinoid, a mound-like swelling on the external surface of the test with the boring at the centre. These would have been moved away from the apical system as the echinoid grew and inserted new plates apically. Whether this infestation was the product of numerous individual organisms or, less likely, just one organism (gastropod?) that relocated when discouraged by each mound-like swelling is uncertain. Similar growth reactions are known from other echinoderms, but associated with non-penetrative Oichnus paraboloides Bromley.  相似文献   
917.
The identification of antigens unique to the positive strain of the tickHyalomma truncatum is discussed. Cattle were separately immunized against sweating-sickness-positive and sweating-sickness-negative ticks. A study was done to demonstrate the difference in protein patterns of crude salivary-gland extracts between positive and negative ticks. Immunological differences were identified using Western blots. A 32 kDa band was found to be unique to the positive strain.  相似文献   
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