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At least 379 records · Page 21Linked to original sources
PubMed1988

Structural and functional integrity of specificity and catalytic sites of trypsin.

The aspartic acid residue at the bottom of the substrate-binding pocket of trypsin was replaced by glutamic acid through site-directed mutagenesis. The wild-type (Asp-189) and mutant (Glu-189) trypsinogens were expressed in E. coli, purified to homogeneity, activated by enterokinase, and tested on a series of fluorogenic tetrapeptide substrates. The substrates were of the general formula succinyl-Ala-Ala-Pro-X-AMC, where AMC is 7-amino-4-methylcoumarin and X is Lys, Arg, or Orn (ornithine). As compared to Asp-189 trypsin, the activity of Glu-189 trypsin on lysyl and arginyl substrates decreased by 3-4 orders of magnitude while its Km values did not significantly change. Lengthening the side-chain of Asp-189 by one methylene group could not be compensated for by shortening the side-chain of the substrate, since Glu-189 trypsin had no measurable activity on the ornithyl substrate. The replacement of Asp-189 with glutamic acid at the base of the substrate-binding pocket of trypsin appears to distort the structure of the critical transition-state complex. This could happen by disrupting interactions normally associated with Asp-189, and by altering the relative position of the scissile peptide bond in the active site of the enzyme.

Aspartic Acid↗
PubMedDate not supplied

Integrated function of urea transporters in the mammalian kidney.

Specific urea transporters are responsible for the rapid urea movements occurring in precise medullary structures of the mammalian kidney. Three of them, ensuring facilitated passive transports, have been cloned yet: UT2-long is responsible for the high vasopressin-dependent urea permeability of the terminal inner medullary collecting ducts; UT2-short is located along a short portion of the thin descending limbs of Henle's loops; UT11 is expressed along the descending vasa recta. These three transporters are involved in the accumulation of urea in the medulla, participating to the corticopapillary osmotic gradient required for urine concentration in the presence of antidiuretic hormone. UT2-long enables diffusion of urea in the inner medulla, and UT2-short and UT11 enable the recycling of this urea by counter-exchange. These transporters could also be involved in nitrogen balance by modulation of their expression according to the need for urea excretion (protein-rich diet), or for nitrogen conservation (protein-poor diet). Several other urea transporters, including active transporters responsible for urea secretion or reabsorption, remain to be cloned and characterized.

Animals↗
PubMed1978

Considerations on the possible structrual basis of neuronal integrated functions.

Different types of dendro-dendritic and dendro-somatic contacts in several species are described. They are classified in five varieties: (a) parallel dendro-dendritic contacts; (b) crossed dendro-dendritic contacts; (c) perisomatic interdendritic contacts; (d) perivascular interdendritic contacts; (e) dendro-somatic contacts. It is hypothetically postulated, in agreement with other authors, that the structurally differentiated interdendritic and dendro-somatic contacts could act as functional junctions for the electrotonic spread of stimuli between neighbour neuronal elements.

Action Potentials↗
PubMedDate not supplied

Online exclusive: functional integration of nursing research into a pediatric oncology cooperative group: finding common ground.

PURPOSE/OBJECTIVES: To provide a brief description of the historic role of nursing and nursing research in the culture of previous pediatric oncology cooperative groups and compare the research language used in cooperative groups with the language used in nursing research. DATA SOURCES: Published empirical, clinical, and methodologic reports. DATA SYNTHESIS: The culture and language of nursing research differ from those of medical research and the pediatric oncology cooperative group, the Children's Oncology Group (COG). Different approaches exist to integrate nursing research priorities into the priorities of COG, including freestanding protocols, companion protocols, and research objectives included in therapeutic protocols. CONCLUSIONS: Full integration of nursing research into COG is feasible but dependent on recognition of cultural and language differences among researchers. Integration will be demonstrated by the number of concepts and protocols contributed to or developed by active nurses in COG. IMPLICATIONS FOR NURSING: Significant advances exist for nurses conducting research in COG. These research efforts are facilitated by a familiarity with the science language used by other disciplines in COG and an understanding of COG's research processes. Increased interdisciplinary scientific collaborations involving nurses in COG particularly benefit pediatric patients with cancer.

Child↗
PubMed1997

Transcriptional activities of estrogen and glucocorticoid receptors are functionally integrated at the AP-1 response element.

Estrogens and glucocorticoids often act in opposition to regulate physiological responses. We investigated whether this might reflect the opposing actions of hormone-bound receptors on target genes regulated by the AP-1 response element. We performed a series of transfection experiments in which transcriptional activation, mediated by the AP-1 response element, was reflected in reporter gene activity. As previously described, we found that estrogens stimulate, whereas the glucocorticoid dexamethasone (Dex) inhibits, transcription through a model promoter from the collagenase gene (-73 to +63). This promoter bears a consensus AP-1 response element. When HeLa cells were treated with both estradiol and Dex, the steroids counteracted each other's transcriptional effects. The amount of transfected estrogen and glucocorticoid receptors (ER and GR) determined the extent to which Dex blunted estrogen stimulation or estrogen prevented Dex inhibition. The ER/GR interaction was observed both in the presence of estradiol and tamoxifen, which has previously been shown to have estrogen-like action at an AP-1 response element. The AP-1 family member c-Jun enhanced Dex inhibition and estradiol stimulation of transcriptional activation. c-Fos potentiated the effect of cotransfected c-Jun on estradiol stimulation but not Dex inhibition. The pattern of steroid responses was retained in the presence of the c-Jun activator phorbol 12-myristate 13-acetate. However, estradiol stimulation was lost in the presence of the c-Jun activator tumor necrosis factor-alpha. The ER/GR/AP-1 response element interaction was present, not only in a cell line originally derived from a uterine cervical adenocarcinoma (HeLa), but also in a cell line derived from the hypothalamus (GT1-1). Lastly, both progesterone receptor types A and B also interacted with the ER at the AP-1 site. These data indicate that opposing steroid influences can be mediated at the level of transcription through the AP-1 site and suggest that the integration of hormone action at this response element may underlie some of the opposing actions of estrogens and glucocorticoids or progestins on physiological responses.

Dexamethasone↗