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1.
Digestion in the cattle-tick Boophilus microplus: light microscope study of the gut cells in nymphs and females 总被引:3,自引:0,他引:3
The gut caeca of B. microplus were studied by light microscopy using paraffin and methacrylate embedded material. It has been shown that during feeding of nymphs and adults, the midgut consists of five cell types, stem cell, digest cell, secretory cells (s1) and (s2) and basophilic cell. The stem cell differentiates into any of the other cell types. The digest cell matures through a series of stages and has up to three generations during feeding on the host. The final generation has two distinct cell types, the first type is thought to be capable of both phagocytosis and pinocytosis. Cells of the second type are predominant at the end of feeding, and may be specialized to ingest and digest haemoglobin. The final stage of the digest series is the spent digest cell which discharges its content into the gut lumen or is excreted whole. The basophilic cell has structures which suggest that one of its functions is to transport digested materials, water and ions across the gut. Secretory cell (s1) secretes a glycoprotein which may be a haemolysin and secretory cell (s2) secretes the gut “colloid” mass, an acid mucopolysaccharide, which may function as an anticoagulant. Intracellular digestion leads to the breakdown of host blood and storage of lipid and glycogen in the digest cells. 相似文献
2.
Basophilic cells in the guts of female ticks are derived from the basal remnants of type 2 secretory cells. As viewed by electron microscopy, these cells have microvilli uniformly distributed on the luminal surface, but they lack the abundant pinocytotic vesicles and lysosomes characteristic of digest cells. The cytoplasm is filled with well organized rough endoplasmic reticulum, Golgi complexes and secretory granules. Infoldings of a basal labyrinth extend the contact of the cell with the underlying haemolymph, and there are many mitochondria in the cell processes between folds. This morphology appears to fit the cell for functioning in active water transport across the gut wall. Subsequent to a final rapid phase of engorgement, the basophilic cell reorganizes its cisternae of rough endoplasmic reticulum into whorls and parallel arrays and resumes a secretory role. 相似文献
3.
Analysis of the lesions in several drug-resistant DNA polymerase mutants of herpes simplex virus along with comparative analysis of the published polymerase sequences of other human herpesviruses has shown that most lesions (five out of six) are substitutions at amino acid residues conserved in all four polymerases. Furthermore, the majority of lesions are in regions of the polypeptide where there are marked clusterings of conserved residues. On the basis of these data we have identified several domains within the polypeptide which we believe may have important functional roles in the action of the enzyme. The apparent restriction in the potential sites of lesions conferring drug resistance may explain the difficulty in selecting such mutants using acyclovir (ACV) in culture and their failure to emerge so far during ACV therapy. Extension of the comparative analysis to the polymerases of adenovirus type 2, vaccinia virus and phage phi 29 suggests that these enzymes also possess domains homologous to those most conserved in the herpes polymerases (regions I-III) and that these domains have a similar linear spatial distribution on the polypeptides. The results are discussed in relation to the known function of the DNA polymerases. 相似文献
4.
Calcitonin receptors of human osteoclastoma 总被引:2,自引:0,他引:2
G C Nicholson M A Horton P M Sexton C S D'Santos J M Moseley B E Kemp J A Pringle T J Martin 《Hormones et métabolisme》1987,19(11):585-589
Osteoclast-rich cultures were prepared by disaggregation of osteoclastomas (giant cell tumour of bone) and settlement onto glass or plastic surfaces. Autoradiography using [125I]-salmon calcitonin ([125I]-sCT) revealed specific binding only to multinucleate giant cells (osteoclasts) and a minor population of mononuclear cells. [125I]-sCT competitive binding studies indicated a Kd of 5 x 10(-10) M and receptor number of approximately 1 million sites/osteoclast. sCT treatment resulted in a dose-dependent rise in cAMP (EC50 10(-10) M). Homogenates of an osteoclastoma also demonstrated specific binding of [125I]-sCT. Chemical cross-linking of a labelled synthetic sCT derivative. [125I]-[Arg11,18,Lys14]-sCT, using disuccinimidyl suberate, resulted in labelling of a receptor component of approximate Mr 85-90,000. The multinucleate giant cells (osteoclasts) of human osteoclastomas possess large number of CT receptors which exhibit the same binding kinetics and apparent Mr as those of other CT target cells. 相似文献
5.
S P Latshaw S Bazaes A Randolph R A Poorman R L Heinrikson R G Kemp 《The Journal of biological chemistry》1987,262(22):10672-10677
The reactivity of the 16 thiol groups of rabbit skeletal muscle phosphofructokinase has been studied extensively over the past 20 years. Several of these thiols show high reactivity with a variety of reagents, display differential reactivity in the presence of allosteric ligands and substrates, and appear to be important to function because their modification changes activity and regulatory properties. In the present study, the location in the primary structure of several highly reactive thiol groups has been established by reaction with [14C]iodoacetate. In the course of these studies, 2 methionyl residues that are located at or near proposed ligand-binding sites are readily carboxymethylated by iodoacetate. In addition to confirming the presence of the most reactive thiol group at sequence position 88, a thiol protected from reaction by the presence of fructose-6-P and cyclic AMP has been found at position 169. Cysteine 169 is close to a residue important to the binding of fructose-6-P in the homologous structure from Bacillus stearothermophilis phosphofructokinase. The modification of Cys-169 brings about extensive, but not total, loss of activity. Another cysteine, at position 232, was found to be highly reactive also. Substrate provided partial protection against carboxymethylation at this position. Carboxymethylation of enzyme restricted to methionines 74 and 173 brought about no changes in the total activity or in the ATP inhibition profile of the enzyme. This is significant since position 74 was projected on the basis of the homologous procaryotic structure to be important in the binding of nucleotide to the allosteric site. 相似文献
6.
Summary Beta-lactam antibiotics supplied at 200 g/mL were rapidly removed from culture fluids of E. coli strains hosting pUR and pEX vectors, indicating that a substantial period of growth occurred in the absence of positive selection. The retention period of the drugs depended on the specific activity and type of the beta-lactamase, the nature of the antibiotic and growth rate of the host. 相似文献
7.
Cattle have been vaccinated againstBoophilus microplus with antigens derived from partially fed female ticks. The immune response of the host lyses the gut cells of adult ticks, causing a reduction in the number, weight and reproductive capacity of engorging ticks. This response is different from the immunity that cattle acquire after repeated tick infestation. Evidence is presented that the antigens used in vaccination are located on the plasma membrane of the gut cells and it is unlikely that these antigens are secreted into the host during feeding. Vaccination using such concealed antigens may not encounter the mechanisms of immune evasion that parasites usually demonstrate.In-vitro assays suggest that vaccination immunity is not dependent on the need to stimulate cell-mediated responses. Immunoglobulin G alone, or with the aid of complement, is enough to damage tick gut.The normal function of the one protein antigen isolated so far is unknown but we speculate that it serves some vital function on the cell plasma membrane. 相似文献
8.
J D Kemp J A Thorson F Gomez K M Smith J S Cowdery Z K Ballas 《Cellular immunology》1989,122(1):218-230
Prior work has suggested that Mabs against the transferrin receptor (ATRAs) may function as selective inhibitors of lymphocyte activation and that T cell activation protocols may be more sensitive to ATRA-mediated inhibition than B cell activation protocols. New side-by-side functional comparisons of three ATRAs are presented. When these studies are considered with our prior work they demonstrate unambiguously that although one particular IgG ATRA consistently fails to inhibit LPS responses and although IgM ATRAs may be slightly more effective inhibitors than IgG ATRAs, ATRAs as a class consistently appear to abolish the MLR at submicrogram concentrations, essentially eliminate cytotoxic cell generation at concentrations between 1 and 5 micrograms/ml, and produce no more than about 50% inhibition of LPS responses at concentrations as high as 25 micrograms/ml. Therefore, an even stronger case can now be made for the idea that lymphocyte subsets differ in their dependence on transferrin receptor function during activation. This, in turn, makes an even stronger case for the idea that lymphocyte subsets differ in fundamental aspects of the management of their iron economies. New studies also show that IgG ATRAs appear to function by causing down-modulation of surface expression of the transferrin receptor in normal lymphocytes in a manner similar to that previously shown for tumor cells. It is clear that a sophisticated model will ultimately be required to account for all of the data arising from studies with ATRAs, and a new attempt at a more detailed construct is presented. 相似文献
9.
A structure-function study of the protein kinase C (PK-C) pseudosubstrate sequence (R19FARK-GALRQKNV31) has been undertaken. The role of specific residues was investigated using an alanine substitution scan. Arg-22 was the most important determinant in the inhibitor sequence, since substitution of this residue by alanine gave a 600-fold increase in the IC50 value to 81 +/- 9 microM. Substitutions of other basic residue also increased the IC50, 5-, 11- and 24-fold for the Ala-19, Ala-23 and Ala-27 substitutions, respectively. The importance of basic residues in determining the potency of the pseudosubstrate peptide reflects the requirements for these residues in peptide substrate phosphorylation. The residues Gly-24, Leu-26 and Gln-28 were also important for pseudosubstrate inhibitor potency. The large difference in the IC50 value for the [A22]PK-C(19-31) peptide makes it a valuable control in studies employing the pseudosubstrate peptide to explore functional roles of PK-C. 相似文献
10.