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961.
The transport of 2-aminoisobutyric acid (AIB) into liver tissue was increased by both insulin and glucagon. We have now shown that these hormones do not stimulate the same transport system. Glucagon, possibly via cAMP, increased the hepatic uptake of AIB by a mechanism which resembled system A. This glucagon-sensitive system could be monitored by the use of the model amino acid MeAIB. In contrast, the insulin-stimulated system exhibited little or no affinity for MeAIB and will be referred to as system B. On the basis of other reports that the hepatic transport of AIB is almost entirely Na+ dependent and the present finding that the uptake of 2-aminobicyclo [2,2,1] heptane-2-carboxylic acid (BCH) was not stimulated by either hormone, we conclude that system B is Na+ dependent. Furthermore, insulin added to the perfusate of livers from glucagon-pretreated donors suppressed the increase in AIB or MeAIB uptake. Depending upon the specificities of systems A and B, both of which are unknown for liver tissue, the insulin/glucagon ratio may alter the composition of the intracellular pool of amino acids. 相似文献
962.
The addition of MC16 tumor cells (a prostaglandin E2-producing cell line induced in C57B1/6J mice by methylcholanthrene) to cultures of normal syngeneic spleen cells inhibits the antibody response of these cells to sheep red blood cells. This inhibition can be blocked by adding to the cultures prostaglandin synthetase inhibitors, such as indomethacin, flufenamic acid and aspirin. These MC16 tumor cells are also immunosuppressive
. Mice bearing the syngeneic MC16 tumor become unresponsive to sheep red blood cells as the tumor grows. As in the
test system, inhibitors of prostaglandin synthetases seem to block the immunosuppressive activity of MC16 cells
since tumor-bearing mice, treated therapeutically with indomethacin, responded normally in their production of antibody to sheep red blood cells. 相似文献
963.
Otto Hansen 《生物化学与生物物理学报:生物膜》1978,511(1):10-22
The effect of the hydrolysis product Pi and the artificial substrate p-nitrophenyl phosphate (p-nitrophenyl-P) on ouabain binding to (Na+ + K+)-activated ATPase was investigated.The hypothesis that (Mg2+ + p-nitrophenyl-P)-supported ouabain binding might be due to Pi release and thus (Mg2+ + Pi)-supported could not be confirmed.The enzyme · ouabain complexes obtained with different substrates were characterized according to their dissociation rates after removal of the ligands facilitating binding. The character of the enzyme · ouabain complex is determined primarily by the monovalent ion present during ouabain binding, but, qualitatively at least, it is immaterial whether binding was obtained with p-nitrophenyl phosphate or Pi.The presence or absence of Na+ during binding has a special influence upon the character of the enzyme · ouabain complex. Without Na+ and in the presence of Tris ions the complex obtained with (Mg2+ + Pi) and that obtained with (Mg2+ + p-nitrophenyl-P) behaved in a nearly identical manner, both exhibiting a slow decay. High Na+ concentration diminished the level of Pi-supported ouabain binding, having almost no effect on p-nitrophenyl phosphate-supported binding. Both enzyme · ouabain complexes, however, now resembled the form obtained with (Na+ + ATP), as judged from their dissociation rates and the K+ sensitivity of their decay. The complexes obtained at a high Na+ concentration underwent a very fast decay which could be slowed considerably after adding a low concentration of K+ to the resuspension medium. The most stable enzyme · ouabain complex was obtained in the presence of Tris ions only, irrespective of whether p-nitrophenyl phosphate or Pi facilitated complex formation. The presence of K+ gave rise to a complex whose dissociation rate was intermediate between those of the complexes obtained in the presence of Tris and a high Na+ concentration.It is proposed that the different ouabain dissociation rates reflect different reactive state of the enzyme. The resemblance between the observations obtained in phosphorylation and ouabain binding experiments is pointed out. 相似文献
964.
The use of a commercial oscillating-tube densitometer with an accuracy of 4 . 10(-7) g/cm3 for the determination of enzyme-kinetics constants is tested. This method is applied to the investigation of the influence of vitamin C (sodium ascorbate) on the glycolytic enzymes invertase, dextransucrase and dextranase. Invertase is inhibited uncompetitively, dextransucrase non-competitively. There is no significant effect of the vitamin on dextranase. The comparison of the mechanisms of the three enzymes suggests that only those reaction steps are inhibited by vitamin C in which fructose is released from the enzyme. 相似文献
965.
By various chemical procedures including ninhydrin-degradation it is shown that the as of yet unknown compound found in partial acid hydrolysates of isolated cell walls of Methanobacterium thermoautotrophicum and other species of this genus is 2-amino-2-deoxy-taluronic acid (N-Acetyltalosaminuronic acid) together with N-acetylglucosamine. It forms the glycan moiety of pseudomurein.Abbreviations PEP
phosphoenolpyruvate
- UDP-GlcNAc
uridindiphospho-N-acetylglucosamine
- MurNAc
N-acetylmuramic acid
- NAcTalNUA
N-acetyltalosaminuronic acid 相似文献
966.
The isolated cell walls of Acetobacterium woodii contain a murein of the crosslinkage type B. d-Orinithinyl residues function as interpeptide bridges between the -carboxyl group of d-glutamic acid and the carboxyl group of the terminal d-analyl residue of an adjacent peptide subunit. The usual l-alanyl residue in position 1 of the peptide subunit is replaced by a l-seryl residue. As yet this murein type was only found in Eubacterium limosum, an organism which was supposed to be related to Acetobacterium because of some metabolic similarities. 相似文献
967.
Otto Vogel 《Developmental biology》1978,67(2):357-370
The egg of the leafhopper Euscelis plebejus has been separated into three fragments [for nomenclature, see Sander, K. (1976). Advan. Insect Physiol.12, 125–238] by two constrictions in order to exclude the middle egg part from possible terminal influences on pattern specification. Middle fragments of freshly laid eggs (two pronuclei or one nucleus) differentiate middle segments of the embryonic pattern. The segment composition of those partial patterns varies with the position of the two constrictions. Eggs subdivided at later stages of development produce similar partial patterns in the middle fragment, but with more segments. The mode of segment expression in single and double fragmented eggs is compatible with the assumption that the metameric pattern is differentiated by a sequence of short-range inductions rather than by an extensive gradient field. 相似文献
968.
C. A. Moreira-Filho A. T. Amaral P. G. Otto A. M. Vianna-Morgante P. A. Otto B. R. Elejalde 《Human genetics》1981,57(4):366-370
Summary H-Y antigen expression was studied on leukocytes and gonad-derived fibroblasts from a patient affected by mixed gonadal dysgenesis. Blood leukocytes and fibroblasts derived from the testis were typed H-Y positive, but the fibroblasts derived from the streak gonad were H-Y negative. Although the patient's karyotype was a mosaic, 45,XO/46,X+mar, as detected in-peripheral blood cells and testis-derived fibroblasts, all the fibroblasts derived from the streak gonad were 45,XO. These data suggests that the marker chromosome was in fact a Y-derived chromosome. Moreover, they showed that, at the gonadal level, a minority of H-Y positive 46,X+mar cells were able to organize a testis. Nevertheless, a large number of XO cells probably did not receive the testicular forming influence of the H-Y antigen and of the other masculinizing factors. 相似文献
969.
Culture-grown astrocytes derived from 3-day-old rat brain were incubated in the presence of [3H]guanosine and of the convulsant agentl-methionine-dl-sulfoximine (MSO). The resulting [3H]tRNA was purified from control and MSO-exposed cells at several time points during the incubation and was hydrolyzed to [3H]guanine and four [3H]methyl guanines which were separated by high pressure liquid chromatography. Three of the four [3H]methyl guanines were more highly labeled in the [3H]tRNA of the MSO-exposed cells, relative to that of the control cells throughout the entire incubation period. The findings extend to cultured astrocytes, the stimulatory effect of MSO on the methylation of neural tRNA guanines, previouly observed both in vitro using [14C]S-adenosyl-l-methionine and in vivo using [methyl
3-H]l-methionine. 相似文献
970.
Mary A. Napier Irving H. Goldberg Otto D. Hensens Ray S. Dewey Jerrold M. Liesch Georg Albers-Schönberg 《Biochemical and biophysical research communications》1981,100(4):1703-1712
On the basis of spectroscopic evidence, opening of a five-membered cyclic carbonate ring (1,3-dioxolan-2-one) in the C15-subunit of the previously determined partial structure (Fig. 1) of the major neocarzinostatin chromophore (NCS-Chrom ), is proposed to account for its base-catalyzed methanolysis to NCS-Chrom . NCS-Chrom , apparently an authentic natural product present as a minor component in all preparations of NCS studied, was found to be formally equivalent to the hydrolysis/decarboxylation product of the cyclic carbonate functionality in NCS-Chrom . The mercaptan-dependent DNA strand-scission activity, equivalent for NCS-Chrom , and , is independent of the integrity of the cyclic carbonate ring system and implicates a secondary site in the C15-substructure for mercaptan activation. 相似文献