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51.
Role of triglyceride-rich lipoproteins and hepatic lipase in determining the particle size and composition of high density lipoproteins 总被引:1,自引:0,他引:1
These studies examined the proposition that the small particle size of HDL3 in the plasma of hypertriglyceridemic subjects is the consequence of the sequential actions of lipid transfer protein and hepatic lipase on HDL. Incubation of unmodified total HDL or HDL3 in the presence of hepatic lipase resulted in a depletion of phospholipid, but little change in the size of the particles. On the other hand, HDL3 that had first been depleted of cholesteryl ester and enriched with triglyceride and phospholipid, during prior incubation with Intralipid and a source of lipid transfer protein, were much more susceptible to the action of hepatic lipase. When these modified HDL3 were incubated with hepatic lipase there was a depletion of the triglyceride and phospholipid content and a conversion into much smaller particles the same size as those predominant in hypertriglyceridemic subjects. These very small particles were derived from a population of modified particles that were larger than the original HDL3 and were within the size range of HDL2. It is proposed, therefore, that in the plasma of hypertriglyceridemic subjects there exists a dynamic balance between the formation of enlarged triglyceride-rich HDL and a secondary conversion of these particles by hepatic lipase to form populations of very small HDL. 相似文献
52.
Genetic and physical characterization of IncM plasmid pBWH1 and its variance among natural isolates 总被引:2,自引:0,他引:2
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J D Hopkins K H Mayer E S Gilleece T F O''Brien M Syvanen 《Journal of bacteriology》1986,165(1):47-52
We present a genetic and physical characterization of the IncM plasmid pBWH1. A physical map was constructed for the enzymes EcoRI, BamHI, SalI, BglII, HindIII, MstII, and XhoI. A series of deletions and a series of subclones of pBWH1 were constructed and used to determine the locations on this map of the transfer region; the replication region; and the genes determining resistance to beta-lactams, chloramphenicol, the sulfonamides, and gentamicin. We compared 51 different isolates, including isolates which had lost individual antibiotic resistances or the transfer phenotype, and showed that variations occurred in all regions of the plasmid genome. Frequently, correlations could be made between phenotypic variation and variation of the EcoRI fragments which contained the gene determining that phenotype. 相似文献
53.
Properties of a serine hydroxymethyltransferase in which an active site histidine has been changed to an asparagine by site-directed mutagenesis 总被引:1,自引:0,他引:1
Histidine 228 at the active site of Escherichia coli serine hydroxymethyltransferase was replaced with an asparagine. The mutant enzyme was expressed in a strain of E. coli that lacks wild type enzyme. Absorption spectra, circular dichroism spectra, and differential scanning calorimetry thermograms suggest that the amino acid change at the active site causes no detectable change in the tertiary structure of the enzyme. Kinetic studies demonstrated that kcat for the mutant enzyme is about 25% of the value for the wild type enzyme with either L-serine or allothreonine as substrate. Km or Kd values for amino acid substrates and reduced folate compounds were 2-10-fold larger with the mutant enzyme. The rate of interconversion of several enzyme-glycine complexes showed that the conversion of the external aldimine to the quinoid complex is not the rate-determining step for either the mutant or wild type enzyme in the presence of tetrahydrofolate. The binding of L-serine to the wild type enzyme gives a more thermally stable enzyme and increases its affinity for tetrahydrofolate. These effects are not found when L-serine binds to the mutant enzyme. The studies demonstrate that histidine 228 is not a catalytically essential residue and suggest that it is involved in interacting with either the amino acid substrate or the enzyme-bound pyridoxal phosphate. 相似文献
54.
Localization of the epidermal growth factor (EGF) receptor within the endosome of EGF-stimulated epidermoid carcinoma (A431) cells 总被引:13,自引:7,他引:6
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K Miller J Beardmore H Kanety J Schlessinger C R Hopkins 《The Journal of cell biology》1986,102(2):500-509
We have followed the internalization pathway of both epidermal growth factor (EGF) and its receptor in human epidermoid carcinoma (A431) cells. Using EGF conjugated with horseradish peroxidase and anti-receptor monoclonal antibodies (TL5 and EGFR1) coupled either directly or indirectly to colloidal gold we have identified an extensive elaboration of endosomal compartments, consisting of a peripheral branching network of tubular cisternae connected to vacuolar elements that contain small vesicles and a pericentriolar compartment consisting of a tubular cisternal network connected to multivesicular bodies. Immunocytochemistry on frozen thin sections using receptor-specific antibody-gold revealed that at 4 degrees C in the presence of EGF, receptors were mainly on the plasma membrane and, to a lesser extent, within some elements of both the peripheral and pericentriolar endosomal compartments. Upon warming to 37 degrees C there was an EGF-dependent redistribution of most binding sites, first to the peripheral endosome compartment and then to the pericentriolar compartment and lysosomes. Upon warming only to 20 degrees C the ligand-receptor complex accumulated in the pericentriolar compartment. Acid phosphatase cytochemistry identifies hydrolytic activity only within secondary lysosomes and trans cisternae of the Golgi stacks. Together these observations suggest that the prelysosomal endosome compartment extends to the pericentriolar complex and that the transfer of EGF receptor complexes to the acid phosphatase-positive lysosome involves a discontinuous, temperature-dependent step. 相似文献
55.
Whole homogenates of bulb mites rapidly metabolized 2-phenylethylamine (PEA) but were appreciably less active against tryptamine, 5-hydroxytryptamine, and dopamine; no degradation of octopamine was detected. The rate of PEA degradation by bulb mites was dependent upon both substrate and homogenate concentrations. PEA degradation was inhibited by pargyline (pI50, 6.7), tranylcypromine (pI50 6.2), and harmaline (pI50 4.1), but not by 5-chloro-2,4-dimethoxyformanilide. These results suggested that PEA metabolism by bulb mite homogenates was catalyzed mainly by Type B monoamine oxidase.Contribution from the Missouri Agricultural Experiment Station, Columbia, MO. Journal Series No. 9777 相似文献
56.
57.
Julie Marcus 《The Australian journal of anthropology》1987,17(3):185-197
Olive Pink studied anthropology at the University of Sydney under Professor A.P. Elkin. Although she did fieldwork among the Northern Aranda and Wailbri of Central Australia, she became disenchanted with anthropology and lived a reclusive life in Alice Springs. In this paper I present a brief outline of her life, particularly during the 1930's I point to the problems she encountered and suggested that she needs to be relocated within her discipline. 相似文献
58.
Winder W. W.; Yang H. T.; Jaussi A. W.; Hopkins C. R. 《Journal of applied physiology》1987,62(4):1442-1447
The purpose of this study was to determine the metabolic function of the marked increase in plasma epinephrine which occurs in fasted rats during treadmill exercise. Fasted adrenodemedullated (ADM) and sham-operated (SHAM) rats were run on a rodent treadmill (21 m/min, 15% grade) for 30 min or until exhaustion. ADM rats were infused with saline, epinephrine, glucose, or lactate during the exercise bouts. ADM saline-infused rats showed markedly reduced endurance, hypoglycemia, elevated plasma insulin, reduced blood lactate, and reduced muscle glycogenolysis compared with exercising SHAM's. Epinephrine infusion corrected all deficiencies. Glucose infusion restored endurance run times and blood glucose to normal without correcting the deficiencies in blood lactate and muscle glycogenolysis. Infusion of lactate partially corrected the hypoglycemia at 30 min of exercise, but endurance was not restored to normal and rats were hypoglycemic at exhaustion. We conclude that in the fasted exercising rat, actions of epinephrine in addition to provision of gluconeogenic substrate are essential for preventing hypoglycemia and allowing the rat to run for long periods of time. 相似文献
59.
G. Gray Eaton Deanne F. Johnson Barbara B. Glick Julie M. Worlein 《Primates; journal of primatology》1986,27(2):141-150
We have quantitatively documented the development of sex differences in the behavior of juvenile Japanese macaques (1 to 2
years of age). Mothers treated their offspring differently by sex, i.e., mothers of males broke contact with them more frequently
than did mothers of females. Juvenile males played more, and mounted other macaques more frequently; juvenile females groomed
their mothers more and were also punished by other group members more frequently than were males. Males showed a pattern of
decreasing interactions with their mothers, but females increased the frequency of their maternal interactions. These patterns
appear to presage the life histories of the sexes. However, comparisons with other species of nonhuman primates indicate that
although sex differences in behavior are common, the variability among species severely limits cross-specific generalizations. 相似文献
60.
Barbara Beckerman Glide G. Gray Eaton Deanne F. Johnson Julie Worlein 《International journal of primatology》1986,7(2):139-155
The behavioral interactions of 22 infant and mother Japanese macaques with other group members were studied. Focal-animal
observations were made from the time of each infant’s birth until 1 year of age. Infants and mothers both displayed exceedingly
strong preferences for associating with matrilineal kin and, specifically, for female kin. The degree of genetic relatedness
was positively correlated with levels of spatial proximity, contact, grooming, aggression, and play. Overall frequencies of
interactions with nonkin were very low, and partner sex was not an important factor in interactions with nonkin. There were
no significant differences between male and female infants in interactions with kin versus nonkin. There was only one significant
difference between male and female infants in interactions with males versus females: female infants showed stronger preferences
for initiating proximity with females over males than did male infants. Because mothers provide the focal point for infant
interactions during the first year of life, we compared the behavior of infants and mothers. Mothers were the recipients of
more social interactions than were infants, mothers engaged in more grooming than did infants, and infants engaged in more
social play than did mothers. These findings are only partially consistent with kin-selection theory, and the inadequacies
of studying matrilineal kin discrimination to test kin selection are reviewed. The near-absence of infant sex differences
in associations with social partners suggests that although maternal kin other than the mother are important to infant socialization,
they probably do not contribute to the development of behavioral sex differences until after the first year of life. 相似文献