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91.
Fred C. June 《Environmental Biology of Fishes》1977,2(3):285-296
Synopsis The timing of ovarian maturation and spawning of 17 warmwater fish species in Lake Oahe (South and North Dakota) was estimated from changes in the mean ovary indices (ratios of ovary weight to fish length). The onset of vitellogenesis varied within species (up to 2 months). Maturation of the ova took from 7.5 to 10 months, depending on species. Annual variations in the mean date of peak spawning of individual species during 1964–1971 were usually less than a week. There was little overlap of the annual mean peak spawning dates of the 17 species, and an established sequence of spawning among species was shown. A relatively high incidence of atresia in the shovelnose sturgeon, northern pike, and carp indicated that these species had apparently not yet adapted to the altered and variable spawning conditions in this reservoir. Regularity of spawning would seem to provide the best chance for spawning success in variable environments such as Lake Oahe. 相似文献
92.
Measurements of stress relaxation in uniaxial extension and associated time-dependent birefringence have been made on bovine fibrin film, prepared by gentle compaction of coarse fibrin clots, containing 13–22% fibrin plasticized with either aqueous buffer or glycerol. Both unligated and ligated (i.e., with α-α and γ-γ ligation by fibrinoligase, factor XIIIa) films were studied. Both types showed two stages of stress relaxation, with time scales of approximately 10 and 103–104 s, respectively, with a plateau region between. In the plateau, the nominal (engineering) stress for ligated glycerol-plasticized film is proportional to In λ, where λ is the stretch ratio, up to λ ? 2, and it decreases with increasing temperature. For unligated glycerol-plasticized film, the stresses are smaller by a factor of one-half to one-third. For ligated film, the second stage of relaxation is relatively slight, and recovery after release of stress is often nearly complete. For unligated film, the second stage involves a substantial drop in stress, and after recovery there is a significant permanent set. A second relaxation for ligated film reproduces the first, but for unligated film it reproduces the first only if the initial relaxation is terminated before the second stage; otherwise, the second relaxation shows a weaker structure. The behavior of water-plasticized film is similar to that of glycerol-plasticized except that the second stage of relaxation occurs at shorter times. During the first stage of stress relaxation, up to about 100 s, the birefringence and the stress-optical coefficient increase; during the plateau zone of stress relaxation, the birefringence of ligated films is approximately constant and is proportional to 2λ2/(λ2 + 1) ? 1, where λ is the stretch ratio. This dependence is predicted by a two-dimensional model in which rodlike elements in the plane of the film are oriented with independent alignment. During the final stage of stress relaxation, the birefringence of ligated films decreases slightly; that of unligated films decreases substantially, but less rapidly than the stress, corresponding to a further increase in the stress-optical coefficient. With additional information from small-angle x-ray scattering reported in an accompanying paper, the first stage of relaxation is attributed to partial release of bending forces in the fibers by orientation, accompanied by increased birefringence. The second stage is attributed, for ligated films, to an internal transition in the fibrin units accompanied by elongation of some of the fibers; and in the unligated films, to a combination of the latter transition with slippage of protofibrils lengthwise within the fiber bundles that causes some loss of orientation, which diminishes the birefringence. 相似文献
93.
The volatile products of vacuum pyrolysis of curdlan are very much influenced by the presence of small proportions of sodium chloride in the polysaccharide during pyrolysis. In the absence of contamination by this salt, the major, volatile products are the 1,6-anhydro-d-glucoses (pyranose and furanose) in 49% yield. Addition of increasing proprtions of sodium chloride decreases the yield of these anhydro-d-glucoses, and causes formation of increasing proportions of 3-deoxy-d-ribo-hexono-1,4-lactone and its d-arabino epimer (i.e., the “glucometasaccharinolactones”) in a combined yield of up to 38%. It is concluded that the pyrolysis of (1→3)-glycans can lead to a “peeling” reaction of the same type as that already known for alkaline degradation. The effect of other salts was also studied. 相似文献
94.
Fred Stutzenberger 《Journal of industrial microbiology & biotechnology》1991,7(4):243-249
Summary Protein-extracted lucerne fiber was used as carbon and energy source for production of extracellular polygalacturonate lyase byThermomonospora curvata. The optimal fiber concentration was 1.5% (w/v); peal lyase activity in culture fluid occurred after 3 days growth at 53°C. During that time, lyase biosynthesis was controlled through induction; production was accelerated by adding small amounts of pectin or by grinding the fiber to 40-mesh particle size to release more inducer. After 3 days growth, lyase activity decreased; inactivation of the enzyme was delayed by the presence of 1 mM Ca or by inhibition of serine proteases with 0.05 mM phenylmethylsulfonyl fluoride. The molecular weight of the lyase produced during growth on the fiber was 35 kDa compared to 56 kDa for the enzyme produced on pure pectin. TheK
m
of the 35-kDa form was 0.54% pectin compared to 0.06% for the 56-kDa form. The smaller form was rapidly inactivated at 60°C, the optimal temperature for activity of the larger form. 相似文献
95.
96.
Aren van Waarde Guido van den Thillart Fred Dobbe 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1982,147(1):53-59
Summary Changes in the concentrations of ammonia, glutamate, alanine, aspartate, -ketoglutarate, oxaloacetate and succinate were measured in freeze-clamped lateralred muscle, dorsal white muscle and liver, and in rapidly cooled blood of goldfish after 12 h of anoxia. Alanine accumulation, succinate accumulation and aspartate depletion are observed in all tissues examined; in the liver the concentrations of glutamate increase and those of ammonia decrease. The mass-action ratio of the glutamate-pyruvate transaminase-catalyzed reaction stays within one order of magnitude from thermodynamic equilibrium in the direction of alanine formation. The mass-action ratio of the glutamate-oxaloacetate transaminase reaction is far from equilibrium when measured oxaloacetate concentrations are used. When levels of free oxaloacetate are calculated from LDH and MDH equilibrium constants, the mass-action ratio of glutamate-oxaloacetate transamination is close to equilibrium in the direction of aspartate formation. Since neither alanine nor glutamate decreases, and since ammonia gradients suggest a continuous ammonia production in all tissues examined, anaerobic proteolysis is assumed. A possible coupling between amino acid catabolism and ethanol production is discussed.Abbreviations
ALA
alanine
-
ASP
aspartate
-
EDTA
ethylene diamine tetraacetate
-
FP
ox
oxidated flavoprotein
-
FP
red
reduced flavoprotein
-
FUM
fumarate
-
GLU
glutamate
-
GOT
glutamate oxaloacetate transaminase
-
GPT
glutamate pyruvate transaminase
-
IMP
inosine monophosphate
- KG
-ketoglutarate
-
LDH
lactate dehydrogenase
-
MAL
malate
-
MAR
mass action ratio
-
MDH
malate dehydrogenase
-
OAA
oxaloacetate
-
PYR
pyruvate
-
sAMP
adenylosuccinate
-
SDH
succinate dehydrogenase
-
SUCC
succinate 相似文献
97.
Summary The intratesticular excurrent duct system of the bull is composed of rete testis, tubuli recti, and the terminal segment of the seminiferous tubules. Each terminal segment is surrounded by a vascular plexus and may be subdivided into a transitional region, middle portion, and terminal plug. The modified supporting cells of the middle portion and the terminal plug no longer display the typical Sertoli-Sertoli junctions seen in the transitional region and the seminiferous tubule proper. In the region of the terminal plug a distinct central lumen is generally not observed: spermatozoa and tubular fluid must pass through an intricate system of communicating clefts between the apices of the closely attached modified supporting cells. Vacuoles in the supranuclear region of the cells in the middle portion indicate strong transepithelial fluid transport. In analogy to the epithelium of rete testis and tubuli recti, the supporting cells of the terminal segment are capable of phagocytosing spermatozoa. The vascular plexus investing the terminal segment serves a dual purpose: it is a regulatory device for fluid and sperm transport, as well as an area of increased diapedesis for white blood cells.Supported by a grant from the Deutsche Forschungsgemeinschaft 相似文献
98.
Surface Changes in Mild Steel Coupons from the Action of Corrosion-Causing Bacteria 总被引:7,自引:4,他引:3 下载免费PDF全文
Christian O. Obuekwe Donald W. S. Westlake Fred D. Cook J. William Costerton 《Applied microbiology》1981,41(3):766-774
Changes which occur on the surface of mild steel coupons submerged in cultures of an Fe(III)-reducing bacterium, isolated from corroded pipe systems carrying crude oil, were studied microscopically to investigate the interaction between the corrosion-causing bacterium and the corroding mild steel coupon. Under micro-aerobic conditions and in the absence of the bacteria, a dense, crystalline, amorphous coat formed on the surface of the steel coupons. In the presence of bacteria the surface coat was extensively removed, exposing the bare metal to the environment. After about 2 weeks of exposure, the removal of the surface coating was followed by colonization of the metal surface by the bacteria. Colonization was mediated by fibrous, exopolysaccharidic material formed by the bacteria. Extension of studies to other bacteria isolated from crude oil and corroded pipes reveals that the formation of exopolysaccharide fibers and possession of adherent properties are common characteristics of bacteria from crude oil systems. 相似文献
99.
Fred Punzo 《Journal of experimental marine biology and ecology》1982,60(1):71-76
The role of external calcium ions in the fertilization of the sea urchin, Strongylocentrotusfranciscansus (A. Agassiz), was studied. When eggs were inseminated with jelly-treated sperm in artificial sea waters containing various concentrations of calcium, the percentage of fertilization decreased with decreasing concentrations of calcium. A small amount of external calcium ions was also found to be essential for fertilization by spermatozoa with reacted acrosomes. The binding capacity of jelly-treated spermatozoa to eggs was, however, not adversely affected by a calcium deficiency. These results suggest that calcium ions are required not only for the initiation of the acrosome reaction, but also for successful levels of fertilization following sperm-binding to eggs even after the acrosome reaction has occurred. 相似文献
100.
John I. Stiles Linda R. Friedman Cynthia Helms Sandra Consaul Fred Sherman 《Journal of molecular biology》1981,148(4):331-346
A mutant of the yeast Saccharomyces cerevisiae contains an increased amount of iso-1-cytochrome c because two copies of a segment, denoted COR, were transposed to a new position on chromosome VII, while the original COR region was retained at the normal position on chromosome X; this COR segment encompasses the CYC1, OSM1 and RAD7 loci which determine, respectively, iso-1-cytochrome c, osmotic sensitivity and ultraviolet light sensitivity. The analysis of genomic DNA with cloned probes indicates that the length of the COR segment is approximately 12,000 base-pairs. We suggest that certain normal strains of yeast, which possibly may contain reiterated sequences, can produce extended transpositions similar to prokaryotes. 相似文献