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81.
Domains of receptor mobility and endocytosis in the membranes of neonatal human erythrocytes in the membranes of neonatal human erythrocytes and reticulocytes are deficient in spectrin 下载免费PDF全文
It has previously shown (Schekman, R., and S.J. Singer, Proc. Natl. Acad. Sci. U.S.A. 73:4075-4079) that receptors in the membranes of neonatal human erythrocytes show a restricted degree of lateral mobility, whereas in adult human erythrocytes the receptors are essentially immobile. This restricted mobility is exhibited, for example, when concanavalin A (Con A) induces a limited clustering of its receptors in the neonatal erythrocyte membrane, resulting in the formation of invaginations and endocytic vesicles. This does not happen with adult cells. By the use of indirect immunoferritin labeling of ultrathin frozen sections of Con A-treated neonatal blood cells, we now show that the invaginations and endocytotic vesicles do not stain for spectrin, whereas the adjacent unperturbed membrane is heavily stained. The reticulocytes in the neonatal cell population undergo substantially more Con A-induced invagination and endocytosis than do the erythrocytes. These results lend strong support to the hypothesis that specialized discrete domains exist, or are induced, in the membranes of these neonatal cells, in which receptors are laterally mobile, whereas in the remaining (and predominant) part of the membrane the receptors are immobile. Such mobile domains are characterized by an absence of spectrin. During the maturation of the neonatal reticulocyte to erythrocyte, it is proposed that these domains are in large part, but not completely, eliminated. 相似文献
82.
Richard L. Marsh Steven J. Wickler 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1982,149(1):99-105
Summary We examined the transition from ectothermy to endothermy in nestling bank swallows (Riparia riparia) by measuring the peak metabolic response to cold (PMR) in groups of nestlings. Additionally aerobic capacity, as assessed by citrate synthase activity (CS), and contractile function, as assessed by myofibrillar ATPase activity (mATPase) were measured in the pectoralis and mixed leg muscles during development. During the first 65% of their growth (from 2–12 g) bank swallows do not increase their metabolic rate in response to cold (Fig. 1). Between 12 and 16 g the PMR increased from 4 to more than 10 ml O2 (g·h)–1. Citrate synthase activity increased throughout development, starting at 20 moles (min·g fresh mass)–1 in both tissues and increasing to 150 and 50 moles (min·g)–1 in the pectoralis and leg muscles, respectively (Fig. 5). The augmented aerobic capacity combined with large increases in muscle mass undoubtedly contributes to the improved thermoregulatory abilities of older nestlings. However, muscle mass and aerobic capacity increase continuously and do not show the sharp transition noted in PMR. In the leg muscle mATPase activity is constant throughout growth, but in the pectoralis muscle it undergoes an abrupt increase from 0.5 moles (min·mg myofibrillar protein)–1 in animals weighing less than 12 g to 0.9 moles (min·mg)–1 in nestlings weighing more than 15 g (Fig. 6). The similar pattern of development of PMR and mATPase suggests a critical role for muscle development in the transition to endothermy in this species.Abbreviations
CS
citrate, synthase
-
mATPase
myofibrillar adenosine triphosphatase
-
PMR
peak metabolic rate during cold stress
-
rate of oxygen consumption 相似文献
83.
B A Horwitz S J Wickler 《Proceedings of the Society for Experimental Biology and Medicine. Society for Experimental Biology and Medicine (New York, N.Y.)》1983,173(1):35-40
Catecholamine-induced thermogenesis is significantly diminished in BIO 14.6 cardiomyopathic hamsters as demonstrated by a reduced increase in oxygen consumption of these hamsters in response to administered isoproterenol. This decreased responsiveness is accompanied by a reduction in the amount of brown adipose tissue, a major nonshivering thermogenic effector. The present study demonstrates that the metabolic responses of individual brown fat cells are also altered in the dystrophic hamster. That is, 1 microM norepinephrine, the physiological mediator of nonshivering thermogenesis, evoked rates of oxygen consumption that were significantly lower in brown adipocytes isolated from the BIO 14.6 hamsters than in those from normal controls. Additionally, the dystrophic adipocytes exhibited: decreased maximal activity (per cell as well as per milligram protein) of citrate synthase; decreased cell size; and decreased amounts of protein per cell. These data indicate that the nonshivering thermogenic capacity of the intact BIO 14.6 hamsters reflects altered characteristics of the individual brown adipocytes themselves, as well as decreased amounts of the tissue. 相似文献
84.
85.
Greg J Poet Ojore BV Oka Marcel van Lith Zhenbo Cao Philip J Robinson Marie Anne Pringle Elias SJ Arnér Neil J Bulleid 《The EMBO journal》2017,36(5):693-702
Folding of proteins entering the secretory pathway in mammalian cells frequently requires the insertion of disulfide bonds. Disulfide insertion can result in covalent linkages found in the native structure as well as those that are not, so‐called non‐native disulfides. The pathways for disulfide formation are well characterized, but our understanding of how non‐native disulfides are reduced so that the correct or native disulfides can form is poor. Here, we use a novel assay to demonstrate that the reduction in non‐native disulfides requires NADPH as the ultimate electron donor, and a robust cytosolic thioredoxin system, driven by thioredoxin reductase 1 (TrxR1 or TXNRD1). Inhibition of this reductive pathway prevents the correct folding and secretion of proteins that are known to form non‐native disulfides during their folding. Hence, we have shown for the first time that mammalian cells have a pathway for transferring reducing equivalents from the cytosol to the ER, which is required to ensure correct disulfide formation in proteins entering the secretory pathway. 相似文献
86.
Genes essential for the production of a linear, bacterial (1-->3)-beta-
glucan, curdlan, have been cloned for the first time from Agrobacterium sp.
ATCC31749. The genes occurred in two, nonoverlapping, genomic fragments
that complemented different sets of curdlan( crd )-deficient
transposon-insertion mutations. These were detected as colonies that failed
to stain with aniline blue, a (1-->3)-beta-glucan specific dye. One
fragment carried a biosynthetic gene cluster (locus I) containing the
putative curdlan synthase gene, crdS, and at least two other crd genes. The
second fragment may contain only a single crd gene (locus II).
Determination of the DNA sequence adjacent to several locus I mutations
revealed homology to known sequences only in the cases of crdS mutations.
Complete sequencing of the 1623 bp crdS gene revealed highest similarities
between the predicted CrdS protein (540 amino acids) and glycosyl
transferases with repetitive action patterns. These include bacterial
cellulose synthases (and their homologs), which form
(1-->4)-beta-glucans. No similarity was detected with putative
(1-->3)- beta-glucan synthases from yeasts and filamentous fungi.
Whatever the determinants of the linkage specificity of these beta-glucan
synthases might be, these results raise the possibility that
(1-->3)-beta-glucans and (1-->4)-beta-glucans are formed by related
catalytic polypeptides.
相似文献
87.
Wolfgang Wickler 《Ethology : formerly Zeitschrift fur Tierpsychologie》1980,52(2):201-209
A possible mechanism is suggested that would link pair-specific dueting to pairbonding as an adaptive strategy. Working out a complex duet is interpreted as a kind of investment, more advantageous than other pre-mating investments and satisfying the partner's coyness. 相似文献
88.
89.
Irenus Eibl-Eibesfeldt Wolfgang Wickler 《Ethology : formerly Zeitschrift fur Tierpsychologie》1968,25(6):719-726
Ein althergebrachter Typ südbalinesischer Statuen, “Mömmedi” genannt, wird beschrieben. Untersuchungen an Ort und Stelle ergaben, daß es zum Schutz von Haus und Eigentum aufgestellte Wächterfiguren sind. Sie senden mehrere soziale Drohsignale, nämlich das Präsentieren des erigierten Phallus und manchmal auch des Analfeldes, eine offen hochgehaltene Hand und ein Drohgesicht. 相似文献
90.