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21.
22.
Role of Magnesium in the Binding of Substrate and Effectors to Phosphoenolpyruvate Carboxylase from a CAM Plant 总被引:2,自引:2,他引:0 下载免费PDF全文
The binding of phosphoenolpyruvate, malate, and glucose 6-phosphate to phosphoenolpyruvate carboxylase purified from Crassula argentea Thunb. was measured using both the intrinsic tryptophan fluorescence of the enzyme and the extrinsic fluorescence of the complex of 8-anilino-1-napthalenesulfonate with the enzyme. It was found that the substrate phosphoenolpyruvate can bind in the absence of magnesium but is bound in greater quantities and more tightly when magnesium is present. Malate reduces the binding of phosphoenolpyruvate, while glucose 6-phosphate increases the binding of the substrate. Glucose 6-phosphate requires magnesium to bind to the enzyme, while malate does not. The general trends from the binding experiments using fluorescence methods were confirmed by activity determinations using assays performed in the absence of magnesium. 相似文献
23.
Heterogeneity in lymphocyte spectrin distribution: ultrastructural identification of a new spectrin-rich cytoplasmic structure 总被引:9,自引:7,他引:2 下载免费PDF全文
Spectrin-like proteins are found in a wide variety of non-erythroid cells where they generally occur in the cell cortex near the plasma membrane. To determine the intracellular distribution of alpha-spectrin (alpha-fodrin) in lymphocytes, we have developed an immunoperoxidase method to localize this protein at the ultrastructural level. Of considerable interest, particularly with regard to our efforts to determine the function of spectrin in this cell type, was the finding that its subcellular localization and its relationship with the plasma membrane can vary dramatically. Based on its position in the cell, alpha-spectrin can occur in two forms in lymphocytes: one that associates closely with the plasma membrane and another that occurs at some distance from the cell periphery, either as a single large aggregate or as several smaller ones. The single large aggregate of spectrin is a stable feature in a number of lymphocyte cell lines and hybrids which were used to examine its ultrastructural characteristics. A previously undescribed cellular structure, consisting of a meshwork of spectrin filaments and membranous vesicles, was identified in these cells. This structure could be induced to dissipate in response to membrane perturbants (e.g., hyperthermia and phorbol esters, known effectors of lymphocyte function and differentiation) and the patterns resulting from the redistribution of spectrin were a reflection of those observed routinely in lymphocytes in situ. The correlation between naturally occurring spectrin localization patterns and those seen after membrane perturbation suggested the possibility that spectrin distribution is indicative of particular maturation stages or functional states in lymphocytes. The implications of these findings with regard to the role of spectrin in lymphocyte function are discussed. 相似文献
24.
Fructose 2,6-bisphosphate inhibits phosphoglucomutase noncompetitively with respect to the cofactor glucose 1,6-bisphosphate. Previous studies from our laboratory had shown that phosphoglucomutase was activated by fructose 2,6-bisphosphate in the absence of added glucose 1,6-bisphosphate. The fructose 2,6-bisphosphate activation previously reported was due to the presence of glucose 1,6-bisphosphate in the commercial preparation of fructose 2,6-bisphosphate. 相似文献
25.
P L Black H Phillips H R Tribble R Pennington M Schneider J E Talmadge 《Journal of cellular biochemistry》1988,36(4):377-392
The mechanism of therapeutic activity of recombinant murine interferon-gamma (rMu IFN-gamma) and the IFN inducer polyinosinic-polycytidylic acid solubilized with poly-L-lysine in carboxy methyl cellulose (pICLC) in treating metastatic disease was investigated by comparing effector cell augmentation with therapeutic activity in mice bearing experimental lung metastases (B16-BL6 melanoma). Effector cell functions in spleen, peripheral blood, and lung (the organ with tumor) were tested after 1 and 3 weeks of rMu IFN-gamma or pICLC administration (intravenous, three times a week). In these studies, natural killer (NK), lymphokine-activated killer (LAK), cytolytic T lymphocytes (CTL) (against specific and nonspecific targets), and macrophage tumoricidal and tumoristatic activities were measured. rM IFN-gamma and pICLC had therapeutic activity and immunomodulatory activity in most assays of immune function examined. Specific CTL activity of pulmonary parenchymal mononuclear cells (PPMC), but not in splenocytes or peripheral blood lymphocytes (PBL), during week 3 and not during week 1, correlated with the therapeutic activity of rMu IFN-gamma and of pICLC. Macrophage tumoricidal activity in PPMC, but not in alveolar macrophages, also correlated with the therapeutic activity of rMu IFN-gamma, but the opposite was true for the therapeutic activity of pICLC. NK activity of PPMC, but not of splenocytes or PBL, during week 1 correlated with the therapeutic activity of pICLC; in contrast, NK activity at any site did not correlate with the therapeutic activity of rMu IFN-gamma. LAK activity at any site did not correlate with the therapeutic activity of either agent. 相似文献
26.
Functional organ bath experiments and radiolabelled ligand binding studies were used to investigate the relationship between beta-adrenoceptor-mediated relaxation and the total number of beta-adrenoceptors in human lung parenchymal tissue and bronchial tissue. Sensitivity to the beta-adrenoceptor agonist isoprenaline (pD2) varied almost 10-fold (pD2 values 6.00 to 6.85) for lung parenchymal preparations and 35-fold for bronchial preparations (pD2 values 6.16 to 7.67) between patients. The total number of [3H] DHA labelled beta-adrenoceptors (Bmax) varied almost 6-fold for lung parenchymal membrane preparations (Bmax 164 to 936 fmol/mg protein) and less than 2-fold for bronchial tissue membrane preparations (Bmax 188 to 342 fmol/mg protein) between patients. Comparison of sensitivity to isoprenaline and beta-adrenoceptor number for lung parenchymal tissue from the same patient demonstrated a negative correlation (r = -0.80 [95% confidence intervals: -0.13, -0.96], 6 d.f., P less than 0.05), suggesting that beta-adrenoceptor-mediated sensitivity of lung parenchymal tissue is inversely related to the number of beta-adrenoceptors. However, there was an absence of correlation between sensitivity to isoprenaline and beta-adrenoceptor number in bronchial tissue from the same patient. Thus, the findings of the present study do not support the possibility of a direct relationship between the beta-adrenoceptor-mediated responsiveness and the beta-adrenoceptor number of human airway preparations. 相似文献
27.
Black VH 《The Journal of steroid biochemistry and molecular biology》1992,43(8):863-868
Several cytochrome P450s have been identified in guinea pig adrenal microsomes which are distinct from the known steroidogenic P450s, c17 and c21, and are immunochemically related to cytochrome P450s found in liver. One, a 52 K protein related to P450 I (CYP1), occurs almost exclusively in males, is localized to the inner zone, and is suppressed by ACTH. Its levels correlate with microsomal capacity for xenobiotic metabolism. The others, related to P450s II and III (CYP2 and 3), are more predominant in males, but not exclusive to them, are found in both the inner and outer zones, and are not suppressed by ACTH. Their functions remain to be elucidated. The male predominance of the CYP1-related protein has recently been shown to be due to suppression of the protein in females by estrogen. To determine if estrogen is also involved in the regulation of the CYP2-related proteins, ovariectomized and sham-operated animals were treated with a long-acting estrogen, estradiol valerate, or with the vehicle alone. These P450s reached male levels in ovariectomized females treated only with the vehicle. Their enhanced levels were suppressed by treatment with estrogen. Estrogen treatment also suppressed the levels of the P450s seen in sham-operated females. Endogenous estrogen produced similar effects. In hemi-ovariectomized females the contralateral ovary hypertrophied, a state in which estrogen levels would be maintained or increased. In these females no increase occurred in the immunodetectable P450s. In normal females, estrogen levels are low in prepubertal animals, rise at the time of puberty and drop again after ovarian cycling is completed. The CYP2-related proteins were present in adrenal microsomes of prepubertal females, but were suppressed after puberty. On the other hand, post-estrous females, in whom estrogen levels would be low, acquired male levels of these proteins in their adrenal microsomes. P450c17 and P450c21, as well as 3β-hydroxysteroid dehydrogenase, were not affected by surgery or estrogen. Taken together, these experiments indicate that suppression by estrogen in females can account, in large part, for the predominance of several immunochemical homologs of liver P450s in adult male guinea pig adrenals. 相似文献
28.
K Sakatani J A Black J D Kocsis 《Proceedings. Biological sciences / The Royal Society》1992,247(1319):155-161
GABA (gamma-aminobutyric acid) is a major inhibitory synaptic neurotransmitter with widespread distribution in the central nervous system (CNS). GABA can also modulate axonal excitability by activation of GABAA receptors in CNS white matter regions where synapses and neuronal cell bodies are not present. Studies on cultured glia cells have revealed the synthesis of GABA in rat optic nerve O-2A progenitor cells that give rise to oligodendrocytes and type 2 astrocytes in vitro. We report here that: (i) GABA is detected by immuno-electron microscopy in intact rat optic nerve and is localized to glia and pre-myelinated axons during the first few weeks of postnatal development, but is markedly reduced or absent in the adult; and (ii) neonatal optic nerve is depolarized by GABAA receptor agonists or by the inhibition of GABA uptake. These results demonstrate the presence of functional GABAA receptors, and GABA uptake and release mechanisms in developing rat optic nerve, and suggest that excitability of developing axons can be modulated by endogenous neurotransmitter at non-synaptic sites. 相似文献
29.
W F Colebrook J L Black G H Brown J B Donnelly 《Australian journal of biological sciences》1988,41(2):201-214
The relative importance of cell number and cell size in determining the mass of 16 organs and tissues in mature rams of six different breeds was studied through estimation of organ deoxyribonucleic acid (DNA) content. The mean fleece-free empty body weight (FFEBW) ranged from 54.6 +/- 0.3 kg for Camden Park Merinos to 76.7 +/- 1.6 kg for Strong Wool Merinos. For all organs, mass increased with FFEBW, but the relationship was significant across all sheep for only eight organs (blood, kidney, liver, abomasum, vastus lateralis muscle, skin, perirenal fat and triceps muscle). There were significant differences between breeds in the mass of 11 organs. With four (heart, rumen reticulum, small intestine and testicular fat) this difference was independent of breed differences in FFEBW, whereas with another four (kidney, abomasum, vastus lateralis muscle and skin), it was closely related to FFEBW. Breed differences in the mass of the remaining three organs (blood, liver and perirenal fat) were partly related to FFEBW and partly breed specific. Blood mass increased with FFEBW across all animals, but, within a breed, it declined as FFEBW increased. The increase in the mass of perirenal fat with FFEBW was significantly greater within a breed than between breeds. Cell number increased significantly with the mass of all organs except blood and brain. There were between-breed differences in the number of cells in seven organs (liver, heart, rumen reticulum, abomasum, small intestine, vastus lateralis muscle and skin), which, except for heart, were attributable to between-breed differences in organ mass. With heart, the increase in cell number with organ mass within a breed was greater than across all breeds. Cell size was significantly related to organ mass only with vastus lateralis muscle, spleen, perirenal fat and liver. The relationship for vastus lateralis muscle and spleen was negative, indicating that cells were smaller in larger organs. There were differences between breeds in cell size for heart, vastus lateralis and triceps muscles. These differences for heart and triceps muscle were breed specific, whereas for vastus lateralis muscle it was attributed to breed differences in organ weight. There was a 30-fold range in mean cell size across organs, with adipose tissue having the largest cells, muscle tissue intermediate and visceral tissues the smallest. In general, organ mass is positively related to FFEBW. Cell number, not cell size, is largely responsible for differences in organ mass between mature sheep of different breeds. 相似文献
30.
Organosolv pretreatment for enzymatic hydrolysis of poplars: I. Enzyme hydrolysis of cellulosic residues 总被引:2,自引:0,他引:2
Chum HL Johnson DK Black S Baker J Grohmann K Sarkanen KV Wallace K Schroeder HA 《Biotechnology and bioengineering》1988,31(7):643-649
Aspen (Populus tremuloides) and black cottonwood (Populus trichocarpa) organosolv pulps produced in a wide range of solvent composition (between 30 and 70% by volume of methanol) and catalysts (H(2)SO(4) and H(3)PO(4)) such that the cooking liquor pH = 3 are easily digested by enzymes. The total yields of hydrolysis residues (pulps) are in the 40-60% range; the acid-catalyzed delignification followed by enzyme hydrolysis can generate 70-88% of the original six-carbon sugars contained in the wood. Glucomannan and arablnogalactan are dissolved into the pulping liquor in the pH range of 2-4.5. Lower pH (=3) leads to additional solubilization of six-carbon sugars. These sugars may be fermented directly. From the insoluble hydrolysis residues, 36-41% conversions of wood into fermentable sugars were obtained after enzyme hydrolysis; the starting feedstocks contain 50.8 and 46.6% hexosans, respectively, for aspen and black cotton-wood. The kinetics of enzymatic hydrolysis of cellulose can be formally treated as two simultaneous pseudo-first-order reactions in which fast and slow hydrolyses of cellulose occur. Correlations between the glucan digestibility and the effect of the pretreatment have been made. The higher residual xylan content reduces the amount of the rapidly hydrolyzable glucan fraction and lowers the glucan digestibility. The proposed simple kinetic treatment is very helpful in assessing the effect of the pretreatment on pulp enzyme hydrolyzability. 相似文献