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排序方式: 共有338条查询结果,搜索用时 15 毫秒
1.
D. R. Anderson K. P. Burnham B. R. Crain 《Biometrical journal. Biometrische Zeitschrift》1985,27(7):723-731
ANDERSON and POSPAHALA (1970) investigated the estimation of wildlife population size using the belt or line transect sampling method and devised a correction for bias, thus leading to a class of estimators with desirable characteristics. This work was given a basic and rigorous mathematica framework by BURNHAM and ANDERSON (1976). In the present article we use this mathematical framework to develop an estimator of population size and density using weighted least squares. The approach is a two-stage Method. 相似文献
2.
3.
Dose Response Curve Linearization and Computer Potency Calculation of Turbidimetric Microbiological Vitamin Assays
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The dose response curves of various turbidimetric microbiological assays, including vitamin B12, Ca pantothenate, and pyridoxine (vitamin B6), were linear with logarithmic transformation of the responses by use of the equation derived, ln[T(x) - T(∞)] = ln A - Bx. A Fortran computer program which used the slope ratio potency calculation was written. The assay potencies calculated by the computer program showed excellent agreement with those obtained by the manual calculation. 相似文献
4.
The incubation of beta-carotene-(14)C with the soluble fraction of the intestinal mucosa resulted in the formation of small amounts of acidic material. The addition of NAD or NADH to the soluble fraction caused a tenfold increase in this material. Incubation of retinal-15-(14)C with the soluble fraction of the intestinal mucosa plus NAD or NADH resulted in the conversion of 80-90% of the retinal to acidic material, which has been shown to contain retinoic acid. In vivo studies on the formation of retinoic acid in the intestinal mucosa after the administration of beta-carotene-(14)C revealed that an appreciable amount of beta-carotene was converted to acidic compounds. When retinal-15-(14)C was administered, portal blood contained 30-40% of the absorbed radioactivity. 24% of this radioactivity was found in acidic material, which has been shown to contain retinoic acid. It is suggested that enzymes in rat intestine cleave beta-carotene to retinal and oxidize the latter to retinoic acid, which is then transported via the portal circulation to the liver. 相似文献
5.
We have broadly defined the DNA regions regulating esterase6 activity in
several life stages and tissue types of D. melanogaster using P-
element-mediated transformation of constructs that contain the esterase6
coding region and deletions or substitutions in 5' or 3' flanking DNA.
Hemolymph is a conserved ancestral site of EST6 activity in Drosophila and
the primary sequences regulating its activity lie between -171 and -25 bp
relative to the translation initiation site: deletion of these sequences
decrease activity approximately 20-fold. Hemolymph activity is also
modulated by four other DNA regions, three of which lie 5' and one of which
lies 3' of the coding region. Of these, two have positive and two have
negative effects, each of approximately twofold. Esterase6 activity is
present also in two male reproductive tract tissues; the ejaculatory bulb,
which is another ancestral activity site, and the ejaculatory duct, which
is a recently acquired site within the melanogaster species subgroup.
Activities in these tissues are at least in part independently regulated:
activity in the ejaculatory bulb is conferred by sequences between -273 and
-172 bp (threefold decrease when deleted), while activity in the
ejaculatory duct is conferred by more distal sequences between -844 and
-614 bp (fourfold decrease when deleted). The reproductive tract activity
is further modulated by two additional DNA regions, one in 5' DNA (-613 to
-284 bp; threefold decrease when deleted) and the other in 3' DNA (+1860 to
+2731 bp; threefold decrease when deleted) that probably overlaps the
adjacent esteraseP gene. Collating these data with previous studies
suggests that expression of EST6 in the ancestral sites is mainly regulated
by conserved proximal sequences while more variable distal sequences
regulate expression in the acquired ejaculatory duct site.
相似文献
6.
Litman GW; Rast JP; Shamblott MJ; Haire RN; Hulst M; Roess W; Litman RT; Hinds- Frey KR; Zilch A; Amemiya CT 《Molecular biology and evolution》1993,10(1):60-72
Immunoglobulins are encoded by a large multigene system that undergoes
somatic rearrangement and additional genetic change during the development
of immunoglobulin-producing cells. Inducible antibody and antibody-like
responses are found in all vertebrates. However, immunoglobulin possessing
disulfide-bonded heavy and light chains and domain-type organization has
been described only in representatives of the jawed vertebrates. High
degrees of nucleotide and predicted amino acid sequence identity are
evident when the segmental elements that constitute the immunoglobulin gene
loci in phylogenetically divergent vertebrates are compared. However, the
organization of gene loci and the manner in which the independent elements
recombine (and diversify) vary markedly among different taxa. One striking
pattern of gene organization is the "cluster type" that appears to be
restricted to the chondrichthyes (cartilaginous fishes) and limits
segmental rearrangement to closely linked elements. This type of gene
organization is associated with both heavy- and light-chain gene loci. In
some cases, the clusters are "joined" or "partially joined" in the germ
line, in effect predetermining or partially predetermining, respectively,
the encoded specificities (the assumption being that these are expressed)
of the individual loci. By relating the sequences of transcribed gene
products to their respective germ-line genes, it is evident that, in some
cases, joined-type genes are expressed. This raises a question about the
existence and/or nature of allelic exclusion in these species. The
extensive variation in gene organization found throughout the vertebrate
species may relate directly to the role of intersegmental
(V<==>D<==>J) distances in the commitment of the individual
antibody-producing cell to a particular genetic specificity. Thus, the
evolution of this locus, perhaps more so than that of others, may reflect
the interrelationships between genetic organization and function.
相似文献
7.
Transduction of light and hormone signals in plants may utilize a mechanism similar to one widely used in animal systems, that of accelerated phosphatidylinositol (PI) turnover. The elements of this central mechanism and consequences of the acceleration as well as recent evidence for its operation in plants are described. 相似文献
8.
Structure determination of a nucleoside Q precursor isolated from E. coli tRNA: 7-(aminomethyl)-7-deazaguanosine. 总被引:5,自引:3,他引:2
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N Okada S Noguchi S Nishimura T Ohgi T Goto P F Crain J A McCloskey 《Nucleic acids research》1978,5(7):2289-2296
A precursor of modified nucleoside Q isolated from E. coli methyl-deficient tRNA was determined to be 7-(aminomethyl)-7-deazaguanosine. The structure was deduced by means of its chromatographic and electrophoretic mobilities, and UV and mass spectra, in addition to comparison with the synthesized authentic compound. The same molecule is also found in tRNA of an E. coli mutant selected for deficient synthesis of modified nucleosides. 相似文献
9.
10.
Inositol phospholipid metabolism may trigger flagellar excision in Chlamydomonas reinhardtii 总被引:3,自引:0,他引:3
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L M Quarmby Y G Yueh J L Cheshire L R Keller W J Snell R C Crain 《The Journal of cell biology》1992,116(3):737-744
Chlamydomonas reinhardtii cells shed their flagella in response to environmental stress. Under favorable conditions, flagella are quickly regrown. To learn more about the signals that trigger flagellar excision and regrowth we have investigated inositol phospholipid metabolites, molecules implicated in signal transduction in several other systems. After deflagellation by low pH or mastoparan, a potent activator of G proteins, there was a rapid increase in levels of inositol 1,4,5-trisphosphate measured by use of receptor-binding assays and HPLC. This increase was concomitant with a decrease in levels of phosphatidylinositol 4,5-bisphosphate and was followed by an increase in phosphatidic acid, results consistent with activation of phospholipase C and diacylglycerol kinase. Additional experiments suggest that this activated phospholipase C is not important for flagellar regrowth but plays a role in informing the excision apparatus of the environmental stress. Addition of neomycin (an inhibitor of phospholipase C) before exposure of cells to low pH or mastoparan prevented the increase in inositol 1,4,5-trisphosphate and also prevented deflagellation. Addition of neomycin after deflagellation blocked increases in inositol 1,4,5-trisphosphate that normally followed deflagellation, but did not block flagellar assembly. Furthermore, a flagellar excision-defective mutant, fa-1, did not shed its flagella in response to low pH or mastoparan, yet both of these agents activated phospholipase C in these cells. The results suggest that activation of phospholipase C, possibly via a G protein, is a proximal step in the signal transduction pathway inducing deflagellation in Chlamydomonas. 相似文献