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Cartilage cathepsin D, cathepsin B and acid phosphatase activities decreased with maturation of Sprague-Dawley rats. Although this phenomenon may largely be due to an age-dependent decrease in cell concentration at young ages (1–8 weeks), in older (8–25 weeks) rats there appeared to be a decrease in enzyme activity per cell. The dimunition in cartilage cathepsin D activity coincided with an apparent decrease in its concentration. In addition, the inverse correlation between rat age and cartilage lysosomal enzyme activities was, at least in part, tissue specific as the pattern of liver lysosomal enzyme activities was quite different from that noted with cartilage. Interestingly, hypophysectomy greatly diminished age-related modulations in lysosomal enzyme activities suggesting that one or more pituitary hormones may be involved in the mechanism of this age-dependent phenomenon. In addition, cartilage growth rate appeared to be correlated with the level of cartilage lysosomal enzyme activities, indicating that these enzymes may be related to the biochemical mechanism of cartilage growth and development. 相似文献
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The rhodopsin system of the squid 总被引:6,自引:19,他引:6
Squid rhodopsin (λmax 493 mµ)—like vertebrate rhodopsins—contains a retinene chromophore linked to a protein, opsin. Light transforms rhodopsin to lumi- and metarhodopsin. However, whereas vertebrate metarhodopsin at physiological temperatures decomposes into retinene and opsin, squid metarhodopsin is stable. Light also converts squid metarhodopsin to rhodopsin. Rhodopsin is therefore regenerated from metarhodopsin in the light. Irradiation of rhodopsin or metarhodopsin produces a steady state by promoting the reactions, See PDF for Equation Squid rhodopsin contains neo-b (11-cis) retinene; metarhodopsin all-trans retinene. The interconversion of rhodopsin and metarhodopsin involves only the stereoisomerization of their chromophores. Squid metarhodopsin is a pH indicator, red (λmax 500 mµ) near neutrality, yellow (λmax 380 mµ) in alkaline solution. The two forms—acid and alkaline metarhodopsin—are interconverted according to the equation, Alkaline metarhodopsin + H+ acid metarhodopsin, with pK 7.7. In both forms, retinene is attached to opsin at the same site as in rhodopsin. However, metarhodopsin decomposes more readily than rhodopsin into retinene and opsin. The opsins apparently fit the shape of the neo-b chromophore. When light isomerizes the chromophore to the all-trans configuration, squid opsin accepts the all-trans chromophore, while vertebrate opsins do not and hence release all-trans retinene. Light triggers vision by affecting directly the shape of the retinene chromophore. This changes its relationship with opsin, so initiating a train of chemical reactions. 相似文献
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Genetic variation at the Major Histocompatibility Complex locus DQ beta was
analyzed in 233 beluga whales (Delphinapterus leucas) from seven
populations: St. Lawrence Estuary, eastern Beaufort Sea, eastern Chukchi
Sea, western Hudson Bay, eastern Hudson Bay, southeastern Baffin Island,
and High Arctic and in 12 narwhals (Monodon monoceros) sympatric with the
High Arctic beluga population. Variation was assessed by amplification of
the exon coding for the peptide binding region via the polymerase chain
reaction, followed by either cloning and DNA sequencing or single-stranded
conformation polymorphism analysis. Five alleles were found across the
beluga populations and one in the narwhal. Pairwise comparisons of these
alleles showed a 5:1 ratio of nonsynonymous to synonymous substitutions per
site leading to eight amino acid differences, five of which were
nonconservative substitutions, centered around positions previously shown
to be important for peptide binding. Although the amount of allelic
variation is low when compared with terrestrial mammals, the nature of the
substitutions in the peptide binding sites indicates an important role for
the DQ beta locus in the cellular immune response of beluga whales.
Comparisons of allele frequencies among populations show the High Arctic
population to be different (P < or = .005) from the other beluga
populations surveyed. In these other populations an allele, Dele-DQ
beta*0101-2, was found in 98% of the animals, while in the High Arctic it
was found in only 52% of the animals. Two other alleles were found at high
frequencies in the High Arctic population, one being very similar to the
single allele found in narwhal.
相似文献
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HUBBARD R 《The Journal of general physiology》1954,37(3):373-379
The respiration of the isolated frog rod outer limb has been measured in the Cartesian diver. The outer limbs respire in Ringer solution without the addition of substrates, but the rate of respiration is increased by the addition of fructose diphosphate or succinate. The respiration is cyanide-sensitive, and therefore presumably mediated by the cytochromes. The Q(OO2) in 0.01 M fructose diphosphate is -1.0 microl. oxygen per mg. dry weight per hour at 20 degrees C. This is lower than the Q(OO2) of whole frog retina, but comparable with it and many other tissues. The respiratory rate is independent of the state of dark adaptation (rhodopsin content) of the outer limbs. The metabolism of the outer limb is probably adequate to provide the DPN required for the maintenance of the rhodopsin concentration necessary for vision. 相似文献
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Can increased niche opportunities and release from enemies explain the success of introduced Yellowhammer populations in New Zealand? 总被引:1,自引:0,他引:1
CATRIONA J. MACLEOD RICHARD P. DUNCAN DAVID M. B. PARISH STEPHEN D. WRATTEN & STEPHEN F. HUBBARD 《Ibis》2005,147(3):598-607
Some introduced species succeed spectacularly, becoming far more abundant in their introduced than in their native range. 'Increased niche opportunities' and 'release from enemy regulation' are two hypotheses that have been advanced to explain the enhanced performance of introduced species in their new environments. Using an introduced bird species, the Yellowhammer Emberiza citrinella , which was first released in New Zealand in 1862, as a model, we tested some predictions based on these hypotheses. By quantifying habitat availability and quality, and measuring nest predation rates, we investigated whether increased niche opportunities or release from nest predation could explain the higher density of the Yellowhammer in New Zealand farmland, compared to farmland in their native Britain. Yellowhammer territory densities were over three times higher in New Zealand (0.40 territories per ha) than in comparable British farmland (0.12 territories per ha), and Yellowhammer densities remained significantly higher in New Zealand, after accounting for differences in habitat availability. The density and diversity of invertebrates, a key food resource for nestling Yellowhammers, was significantly lower in New Zealand than in Britain. Hence, these aspects of niche availability and quality cannot explain the higher density of Yellowhammers in New Zealand. Nest predation rates in New Zealand were similar to those in Britain, suggesting that release from nest predation also could not account for the higher density of Yellowhammers in New Zealand. Differences in winter survival, due to differences in winter food supply or the severity of the winter climate, along with release from other types of 'enemy' regulation are possible alternative explanations. 相似文献
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Significance of nucleotide sequence alignments: a method for random sequence permutation that preserves dinucleotide and codon usage 总被引:10,自引:0,他引:10
The similarity of two nucleotide sequences is often expressed in terms of
evolutionary distance, a measure of the amount of change needed to
transform one sequence into the other. Given two sequences with a small
distance between them, can their similarity be explained by their base
composition alone? The nucleotide order of these sequences contributes to
their similarity if the distance is much smaller than their average
permutation distance, which is obtained by calculating the distances for
many random permutations of these sequences. To determine whether their
similarity can be explained by their dinucleotide and codon usage, random
sequences must be chosen from the set of permuted sequences that preserve
dinucleotide and codon usage. The problem of choosing random dinucleotide
and codon-preserving permutations can be expressed in the language of graph
theory as the problem of generating random Eulerian walks on a directed
multigraph. An efficient algorithm for generating such walks is described.
This algorithm can be used to choose random sequence permutations that
preserve (1) dinucleotide usage, (2) dinucleotide and trinucleotide usage,
or (3) dinucleotide and codon usage. For example, the similarity of two
60-nucleotide DNA segments from the human beta-1 interferon gene
(nucleotides 196-255 and 499-558) is not just the result of their nonrandom
dinucleotide and codon usage.
相似文献
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STEPHEN F. HUBBARD SEAN L. C. O'MALLEY RAYMOND RUSSO 《Medical and veterinary entomology》1988,2(3):279-283
We present an analysis of the functional response of the predator Toxorhynchites rutilus rutilus (Coquillett) to changes in the density of the larvae of Aedes aegypti (L.) (Diptera: Culicidae). The experiment was replicated for five different ages, and at three different densities of the predator. The data were fitted to Rogers' (1972) random predator equation by non-linear least-squares in order to estimate searching efficiency and handling time for each experimental treatment. The data show that estimated searching efficiencies are highest at intermediate ages of the predator for all predator densities tested. Handling time declines exponentially with increasing predator age. There is a marked interference effect; searching efficiency decreases with increased predator density, and this is most pronounced at intermediate prey ages. Estimated handling times increase with predator density at a rate which declines with increasing predator age. 相似文献