Histamine acts directly on human T cells to inhibit interleukin-2 and interferon-gamma production

Histamine acts directly on human T cells to inhibit lymphokine production without the involvement of accessory cells. Histamine inhibits the production of interleukin-2 (IL-2) and interferon-gamma (IFN-gamma) by purified human peripheral T cells activated in the presence of either intact monocytes or metabolically inactive fixed Raji and U698 cells as accessory cells. Purified T cells do not respond more than marginally to staphylococcal enterotoxin A (SEA) or phytohemagglutinin (PHA) in the absence of accessory cells. However, activation by the phorbol ester PMA in conjunction with either PHA or the calcium ionophore A23187 induces large amounts of IFN-gamma and IL-2. Histamine suppresses the lymphokine production in these pure T-cell cultures to a similar extent as in monocyte-containing cultures. Histamine is also shown to suppress DNA synthesis by purified T cells cultivated at a low cell density, eliminating any possible involvement of small numbers of contaminating accessory cells. In vitro preactivated T cells are shown to retain their capacity to respond to histamine when stimulated by PMA and A23187 or by mitogen in the presence of Raji cells. The conclusion that histamine acts directly on T cells and does not require accessory cells to induce suppression is further confirmed by the demonstration that IL-2 production by the human T-cell leukemia line Jurkat was significantly suppressed by histamine in a H-2 receptor-restricted manner.     

Biochemical characterization of histamine-sensitive adenylate cyclase in mammalian brain.

Certain biochemical characteristics of an adenylate cyclase that is activated by low concentrations of histamine (K_a, 8 μm) and that is present in cell-free preparations from the dorsal hippocampus of guinea pig brain have been studied. Histamine increased the maximal reaction velocity of adenylate cyclase without altering the K_m (0.18 mm) for its substrate, MgATP. Increasing concentrations of free Mg²⁺ stimulated enzymatic activity; the kinetic properties of this activation by Mg²⁺ suggest the existence of a Mg²⁺ allosteric site on the enzyme. Histamine increased the affinity of this apparent site for free Mg²⁺. Free ATP was a competitive inhibitor with respect to the MgATP substrate. The apparent potency of free ATP as an inhibitor increased in the presence of histamine. In the presence of Mg²⁺, low concentrations of Ca²⁺ markedly inhibited adenylate cyclase activity; half-maximal inhibition of both basal and histamine-stimulated enzyme activity occurred at 40 μm Ca²⁺. Other divalent cations, including Zn²⁺, Cu²⁺, and Cd²⁺, were also inhibitory. Of the divalent cations tested, only Co²⁺ and Mn²⁺ could replace Mg²⁺ in supporting histamine-stimulated adenylate cyclase activity. The nucleoside triphosphates GTP and ITP increased basal adenylate cyclase activity and markedly potentiated the stimulation by histamine. Preincubation of adenylate cyclase with 5′-guanylylimidodiphosphate dramatically increased enzyme activity; in this activated state, the adenylate cyclase was relatively refractory to further stimulation by histamine or F^?. The subcellular distribution of histamine-sensitive adenylate cyclase activity was studied in subfractions from guinea pig cerebral cortex. The highest total and specific activities were observed in those fractions enriched in nerve endings, while adenylate cyclase activity was not detectable in the brain cytosol fraction. A possible physiological role for this histamine-sensitive adenylate cyclase in neuronal function is discussed.     

Increase of Cu,Zn-superoxide dismutase activity during differentiation of human K562 cells involves activation by copper of a constantly expressed copper-deficient protein.

Cu,Zn-superoxide dismutase activity, expressed on the basis of cell number, increased by 50% during sodium butyrate-induced differentiation of human K562 erythroleukemia cells. The increased enzyme activity was found to be concomitant with constant Cu,Zn-superoxide dismutase mRNA and immunoreactive protein levels and was accompanied by a rise in intracellular copper and glutathione. Incubation of K562 cell homogenates with copper caused an increase of Cu,Zn-superoxide dismutase activity which reached the levels observed after differentiation in the presence of sodium butyrate. The same treatment led to no significant activity increase in homogenates derived from differentiated cells. Externally added ceruloplasmin increased both intracellular copper levels and Cu,Zn-superoxide dismutase activity in undifferentiated cells to a level comparable with that observed after induction of differentiation. Both increments were abolished by depletion of cell glutathione. Cu,Zn-superoxide dismutase purified from control cells had both a lower kcat and a lower copper content than the enzyme purified from differentiated cells. From these data we conclude that: 1) Cu,Zn-superoxide dismutase is present in K562 cells also under the form of a less active copper-deficient enzyme, 2) the extent of enzyme activation is regulated post-translationally by differential delivery of copper as a function of differentiation stage, and 3) glutathione is likely to play a role in delivering copper to the copper-deficient protein in intact K562 cells.     

Uptake and methylation of histamine by dispersed gastric mucosal cells and its possible influence on acid secretion

Inactivation of histamine by gastric mucosal tissue was examined in dispersed rabbit gastric mucosal cells. Mucosal cells were incubated with [14C]histamine. The formed radioactive metabolites were separated and identified by thin layer co-chromatography and quantitated, in both the cellular and extracellular mediums. Gastric mucosal cells internalized histamine, most of which was immediately methylated primarily to N tau-methylhistamine and released. Cellular histamine product accumulation reached a plateau. The rate of histamine methylation increased with increasing extracellular histamine concentration, moving towards a plateau above 5 microM. Histamine methylation was greatly decreased but not abolished at 4 degrees C, in the absence of Na+ and by phlorizin (0.5 mM), an inhibitor of Na(+)-dependent co-transport. Inhibition of histamine N-methyltransferase decreased intracellular methylhistamine content dose dependently without increasing intracellular histamine. The secretagogues pentagastrin and carbachol did not influence histamine metabolism but ethanol inhibited methylation. The data suggest that gastric mucosal cells take up histamine by a Na(+)-dependent and Na(+)-independent process. The histamine uptake capacity appears to be linked to the methylation activity within the cell. The decrease in histamine uptake and metabolism caused by ethanol could potentially increase histamine concentrations near the target cells and be the reason for the stimulatory effect of ethanol on acid secretion.     

Copper regulation of ceruloplasmin in copper-deficient rats.

In copper-deficient rats, oral intubation of copper increases the rate of ceruloplasmin synthesis without affecting general synthesis of plasma or liver proteins. It also restores the enzyme from half to full activity. Copper given by injection at doses commonly employed has additional nonspecific effects on protein synthesis and in some strains of rats produces severe hemolysis. In contrast to deficient rats, in normal rats copper does not elevate plasma ceruloplasmin unless hemolysis also occurs. Thus, at least in deficiency, copper availability controls the rate of synthesis, acitvation, and plasma concentration of ceruloplasmin.     

Evidence that the catalytic and regulatory functions of carbamylphosphate synthetase from Escherichia coli are not dependent on oligomer formation.

Carbamyl-phosphate synthetase from Escherichia coli is an allosteric enzyme which undergoes reversible association reactions in phosphate buffer. The positive allosteric effectors, ornithine, inosine 5'-monophosphate (IMP), and ammonia, facilitate oligomer formation, whereas uridine 5'-monophosphate (UMP), a negative effector, prevents or decreases oligomer formation. When the enzyme is immobilized by reaction with activated Sepharose, under conditions where the enzyme exists only as a monomer, nearly full catalytic activity is retained and the effects of ornithine, IMP, and UMP on the catalytic activity as a function of MgATP concentration are not significantly altered. Gel-filtration chromatography on Sephadex G-200 of catalytic quantities of the enzyme in the presence of all substrates showed that the elution volume was the same as that measured for the enzyme under conditions where it is known to exist in the monomer form. The specific activity of the enzyme does not increase when the concentration of the enzyme is increased 100-fold from a concentration at which the enzyme exists as monomer to a level at which the enzyme exists predominantly as oligomer. These results indicate that the monomer form of the enzyme is the principle active species and that oligomer formation is not directly related to enzyme activity or enzyme regulation.     

Neutrophils and mast cells. I. Human neutrophil-derived histamine-releasing activity

Histamine release occurs during the late phase allergic reaction concomitantly with neutrophil (PMN) infiltration. To determine whether PMN might release a factor capable of causing histamine release, supernatants generated by incubating human PMN in the presence or absence of specific activators were added to rat basophilic leukemia cells (RBL) and histamine release was measured. PMN supernatants from 17 of 21 donors induced noncytotoxic histamine release. Neutrophil-derived histamine-releasing activity, termed HRA-N, was dose-dependent and supernatants from greater than or equal to 10(7) PMN/ml caused 6 to 27% net histamine release from RBL. PMN supernatants induced histamine release as effectively as did intact PMN cocultured with RBL. The capacity of various donors to generate HRA-N was not related to atopic status or gender but was inversely related to the proportion of eosinophils (EOS) contaminating the PMN isolate (the larger the proportion of EOS, the lower the histamine release). Addition of EOS to PMN during the generation of HRA-N completely inhibited histamine-releasing activity. HRA-N was not released from mononuclear cells or platelets contaminating the PMN preparation. HRA-N release was not increased by the presence of either serum-treated zymosan or phorbol myristate acetate, agents that caused dose-related release of PMN granule enzymes. Indeed, HRA-N was released from unstimulated PMN in the complete absence of granule enzyme release. HRA-N release was detectable by 15 min and the majority of release occurred between 45 and 60 min of incubation. Thus, the data indicate that HRA-N is released spontaneously from human PMN and that HRA-N release is independent of primary or secondary PMN granule release. It is attractive to suggest that release of HRA-N by PMN might act to recruit mast cells or basophils into participating in acute inflammatory reactions.     

An X-ray structural study of human ceruloplasmin in relation to ferroxidase activity

The role of ceruloplasmin as a ferroxidase in the blood, mediating the release of iron from cells and its subsequent incorporation into serum transferrin, has long been the subject of speculation and debate. However, a recent X-ray crystal structure determination of human ceruloplasmin at a resolution of around 3.0?Å, in conjunction with studies associating mutations in the ceruloplasmin gene with systemic haemosiderosis in humans, has added considerable weight to the argument in favour of a ferroxidase role for this enzyme. Further X-ray studies have now been undertaken involving the binding of the cations Co(II), Fe(II), Fe(III), and Cu(II) to ceruloplasmin. These results give insights into a mechanism for ferroxidase activity in ceruloplasmin. The residues and sites involved in ferroxidation are similar to those proposed for the heavy chains of human ferritin. The nature of the ferroxidase activity of human ceruloplasmin is described in terms of its three-dimensional molecular structure.     

Cytotoxicity of Vibrio vulnificus cytolysin on rat peritoneal mast cells

Histamine has been thought to be a permeability enhancing factor in Vibrio vulnificus infection. The injection of living bacteria or purified V. vulnificus cytolysin (VVC) can cause lethality in mice by inducing hemoconcentration and increased vascular permeability. In the present study, we tried to identify whether histamine release causes the increased vascular permeability that is responsible for the lethal effect of VVC. Treatment of rat peritoneal mast cells with high concentrations of VVC caused the release of whole cellular histamine and lactate dehydrogenase (LDH). At concentrations less than 10 HU/ml, histamine and LDH were not released whereas preloaded 2-deoxy-D-glucose was rapidly effluxed with the concomitant decrease in cellular ATP. VVC-treated mast cells were refractory to the stimulation of histamine secretion by Compound 48/80 but remained fully responsive to Ca2+ plus GTP-gamma-S. These results indicate that histamine can be released from mast cells only when the concentration of VVC is high enough to cause the lysis of cells. At low concentrations, VVC does not induce the release of stored histamine from damaged cells. The intravenous injection of 80 HU purified VVC to rats, which can produce the calculated blood concentration of about 3 HU/ml, caused a marked increase in pulmonary vascular permeability, hemoconcentration and death. However, no increase in blood histamine level was detected. This level of VVC in rat blood was enough to cause severe hemoconcentration and lethality but might not be enough to cause cytolysis of the mast cells and resulting histamine release.     

Hysteretic behavior of nitrate reductase. Evidence of an allosteric binding site for reduced pyridine nucleotides.

In the absence of NADH, at 25 degrees C, partially purified NADH:nitrate reductase undergoes an approximately 50% reduction of its initial activity during 2 h. With the increase of inactivation, the NADH and nitrite concentration time curves become typical "sigmoidal," i.e. the reaction velocity of the nitrate reductase catalyzed reaction goes through a maximum before equilibrium is reached. About 80% of the original activity of nitrate reductase is restored when the enzyme is incubated for 2 min with 200 microM NADH or NADPH. Also other NADH substrate analogues have similar effects in restoring the lost activity. After incubation with the reduced pyridine nucleotides, the sigmoidal appearance of the NADH concentration time curve disappears almost completely. Despite the fact that NADPH increases the activity of the enzyme, NADPH does not show any competition with the NADH-binding site of nitrate reductase and does not produce nitrite in the absence of NADH. It is therefore concluded that there must be an additional allosteric site which binds either NADH or NADPH, or other pyridine nucleotides with the effect of increasing the activity of the enzyme. A kinetic model is presented which simulates the observed experimental findings.     

Desensitization and recovery of muscarinic and histaminergic Ca2+ mobilization in 1321N1 astrocytoma cells.

Intracellular free Ca2+ was monitored in suspensions of 1321N1 astrocytoma cells by using the Ca2+ indicator fura-2. The cytoplasmic Ca2+ concentration increased from 237 +/- 6 nM to 1580 +/- 170 nM within 3-5 s of addition of 300 microM-carbachol. After the peak in response, the Ca2+ concentration diminished, establishing a new steady state in about 1 min that was approx. 150 nM above the previous baseline. Histamine increased cytoplasmic Ca2+ to about 40% of the maximal value seen with carbachol. In Ca2+-free buffer each agonist elicited a normal initial increase in cytoplasmic Ca2+, but the sustained portion of the response was abolished. The increase in Ca2+ in response to either carbachol or histamine could be completely inhibited by pretreating the cells with carbachol; the response to carbachol could be partially inhibited by pretreating the cells with histamine. The Ca2+ responses did not recover in the continued presence of carbachol. However, if the carbachol was washed out or if atropine was added after carbachol, the responses to agonist recovered in a time-dependent manner (half-time 3-4 min), and recovery depended on the presence of extracellular calcium. The results indicate that carbachol and histamine stimulate release of Ca2+ from the same intracellular Ca2+ store, that depletion of this store is responsible for heterologous desensitization between these two agonists, and that repletion of the agonist-sensitive Ca2+ pool does not occur in the continued presence of agonist or in the absence of extracellular Ca2+.     

Histamine alters E-cadherin cell adhesion to increase human airway epithelial permeability.

During the immediate response to an inhaled allergen, there is an increase in the paracellular permeability of the airway epithelium.1 Histamine is an important agonist released during the immediate response to inhaled allergen. We hypothesized that histamine would increase human airway epithelial paracellular permeability and that it would do this by interrupting E-cadherin-based cell adhesion. Histamine, applied to the basolateral surface, increased the paracellular permeability of cultured human airway epithelia, and this effect of histamine was blocked by the histamine receptor antagonist promethazine. ECV304 cells express a histamine receptor, N-cadherin, and elements of the tight junction, including claudins, but they do not express E-cadherin. Histamine increased the paracellular permeability of ECV304 cells transfected with a vector and expressing E-cadherin but not ECV304 cells expressing lac-Z in the same vector. L cells do not express the histamine receptor, cadherins, or claudins. Histamine decreased adhesion of L cells expressing the human histamine receptor and E-cadherin to an E-cadherin-Fc fusion protein. Histamine did not alter the adhesion to the E-cadherin fusion protein of L cells expressing either the histamine receptor or E-cadherin alone. When applied to the apical surface, adenovirus poorly infects airway epithelial cells because its receptor, CAR, is restricted to the basolateral surface of the cells. When histamine was applied to the basolateral surface of airway epithelial cells, infection of the cells by adenovirus increased by approximately one log. This effect of histamine was also blocked by promethazine. Histamine increases airway paracellular permeability and increases susceptibility of airway epithelial cells to infection by adenovirus by interrupting E-cadherin adhesion.     

Histamine in stress ulcer prophylaxis in rats.

BACKGROUND: Gastrin and its analogues increase the gastric acid secretion, but also enhance mucosal defense mechanisms. On the other hand, increased formation of histamine leading to an increase in gastric acid secretion is accompanied with gastroprotection and acceleration of gastric ulcer healing. AIM: Of this study was to examine the effect of histamine on stress induced gastric ulcers in rats. METHODS: Male Wistar rats were exposed to water immersion and restrain stress (WRS) for 3.5 h at 23 degrees C. Before WRS rats were pretreated with saline, histamine, ranitidine or omeprazole. RESULTS: WRS produces gastric lesions which were strongly reduced by ranitidine or omeprazole. Also treatment with histamine markedly reduced ulcer area evoked by WRS. Addition of histamine to ranitidine or omeprazole caused an additional reduction in ulcer area. Gastroprotective effect of histamine was accompanied with the increase in gastric blood flow (GBF). Administration of omeprazole or ranitidine alone was without significant effect on GBF. Histamine caused an slight decrease in gastric luminal pH, whereas ranitidine or omeprazole significantly increased gastric luminal pH. Plasma interleukin-1beta was significantly reduced after administration of omeprazole, ranitidine, or histamine, however, the effect of histamine was less pronounced. DNA synthesis was increased after administration of omeprazole, ranitidine or histamine when compared with WRS alone. Administration of histamine in combination with ranitidine or omeprazole caused an additional increase in DNA synthesis. CONCLUSIONS: Histamine exhibits protective effect and increases gastroprotective effect of ranitidine and omeprazole against stress-induced gastric lesions. This effect of histamine seems to be independent on gastric acid secretion but related to the increase in gastric blood flow and the reduction in activation of cytokine cascade.     

Histamine is a potent inducer of IL-18 and IFN-gamma in human peripheral blood mononuclear cells

Histamine (10-7 to 10-4 M) concentration-dependently stimulated the production of IL-18 and IFN-gamma and inhibited the production of IL-2 and IL-10 in human PBMCs. Histamine in the same concentration range did not induce the production of IL-12 at all. The stimulatory or inhibitory effects of histamine on cytokine production were all antagonized by H2 receptor antagonists ranitidine and famotidine in a concentration-dependent manner, but not by H1 and H3 receptor antagonists. Selective H2 receptor agonists, 4-methylhistamine and dimaprit, mimicked the effects of histamine on five kinds of cytokine production. The EC50 values of histamine, 4-methylhistamine, and dimaprit for the production of IL-18 were 1.5, 1.0, and 3.8 microM, respectively. These findings indicated that histamine caused cytokine responses through the stimulation of H2 receptors. All effects of histamine on cytokine responses were also abolished by the presence of either anti-IL-18 Ab or IL-1beta-converting enzyme/caspase-1 inhibitor, indicating that the histamine action is dependent on mature IL-18 secretion and that IL-18 production is located upstream of the cytokine cascade activated by histamine. The addition of recombinant human IL-18 to the culture concentration-dependently stimulated IL-12 and IFN-gamma production and inhibited the IL-2 and IL-10 production. IFN-gamma production induced by IL-18 was inhibited by anti-IL-12 Ab, showing the marked contrast of the effect of histamine. Thus histamine is a very important modulator of Th1 cytokine production in PBMCs and is quite unique in triggering IL-18-initiating cytokine cascade without inducing IL-12 production.     

Immunochemical and enzymatic study of ceruloplasmin in rheumatoid arthritis

Forty adult patients (30 women and 10 men) with rheumatoid arthritis (RA), treated with nonsteroidal anti-inflammatory drugs, were studied. Serum levels of immunoreactive ceruloplasmin, oxidase activity of the ceruloplasmin and total copper, as well as the specific oxidase activity (enzyme activity per unit of mass) and the copper/immunoreactive ceruloplasmin relationship were significantly higher in the group of patients than in the healthy control group (p < 0.001). However, no significant difference was found for the concentration of non-ceruloplasmin copper between both groups. A statistically significant negative correlation was obtained for the concentration of serum thiobarbituric acid-reacting substances with the immunoreactive ceruloplasmin and its oxidase activity in the group of patients (p < 0.005). These results suggest that in RA increases of serum copper are produced at the expense of the fraction linked to the ceruloplasmin, diminishing the proportion of apoceruloplasmin and other forms poor in copper. Although the increase in the serum concentration of ceruloplasmin might offer an additional safeguard against oxidative stress. it does not appear to have a beneficial effect upon the activity of the illness as evaluated by means the biological inflammation markers C-reactive protein, erythrocyte sedimentation rate and sialic acid.     

Effect of histamine and cimetidine on retinal and choroidal blood flow in humans

Intravenous administration of histamine causes an increase in choroidal blood flow and retinal vessel diameter in healthy subjects. The mechanism underlying this effect remains to be elucidated. In the present study, we hypothesized that H2 receptor blockade alters hemodynamic effects of histamine in the choroid and retina. Eighteen healthy male nonsmoking volunteers were included in this randomized, double-masked, placebo-controlled two-way crossover study. Histamine (0.32 microg.kg(-1).min(-1) over 30 min) was infused intravenously in the absence (NaCl as placebo) or presence of the H2 blocker cimetidine (2.3 mg/min over 50 min). Ocular hemodynamic parameters, blood pressure, and intraocular pressure were measured before drug administration, after infusion of cimetidine or placebo, and after coinfusion of histamine. Subfoveal choroidal blood flow and fundus pulsation amplitude were measured with laser-Doppler flowmetry and laser interferometry, respectively. Retinal arterial and venous diameters were measured with a retinal vessel analyzer. Retinal blood velocity was assessed with bidirectional laser-Doppler velocimetry. Histamine increased subfoveal choroidal blood flow (+14 +/- 15%, P < 0.001), fundus pulsation amplitude (+11 +/- 5%, P < 0.001), retinal venous diameter (+3.0 +/- 3.6%, P = 0.002), and retinal arterial diameter (+2.8 +/- 4.2%, P < 0.01) but did not change retinal blood velocity. The H2 antagonist cimetidine had no significant effect on ocular hemodynamic parameters. In addition, cimetidine did not modify effects of histamine on choroidal blood flow, fundus pulsation amplitude, retinal venous diameter, and retinal arterial diameter compared with placebo. The present data confirm that histamine increases choroidal blood flow and retinal vessel diameters in healthy subjects. This ocular vasodilator effect of histamine is, however, not altered by administration of an H2 blocker. Whether the increase in blood flow is mediated via H1 receptors or other hitherto unidentified mechanisms remains to be elucidated.     

Release of intestinal diamine oxidase by histamine in rats

Diamine oxidase activity was measured in the intestinal mucosa, lymph, and in the serum of rats, to determine whether histamine, a substrate of diamine oxidase, liberates this enzyme from its mucosal storage site(s). Histamine induced a sharp rise in intestinal lymph flow, lymph protein, and lymph diamine oxidase, lasting less than 1 h after the histamine injection. The rise in lymph diamine oxidase activity was dose dependent over a narrow concentration range (0.05-0.2 mmol/kg, i.v. and 0.15-0.6 mmol/kg i.d.). It did not correlate with the dose dependent increase in lymph flow or lymph protein. A single maximal intraduodenal dose of histamine caused a 41.6-fold increase in the lymph diamine oxidase activity and a 2.4-fold increase in the serum enzyme level temporarily. A second injection of histamine, 2 h after the first, resulted in a comparatively smaller increase in the lymph enzyme. The extent of the reduction was dependent on the magnitude of the first injection. The results suggest that histamine causes a limited liberation of diamine oxidase from the intestinal mucosa. The function of this enzyme release may be a protective response by the mucosa to reduce toxic levels of free histamine, either liberated by the mucosal tissue or absorbed from the intestinal lumen.     

Hemolysis of rabbit erythrocytes in the presence of copper ions

The hemolysis of red blood cells (RBC) induced by Cu(II) is modified by ceruloplasmin (Cp) and albumin. The time course of hemolysis for rabbit RBC by Cu(II) consisted of two parts, an induction period followed by a catastrophic lysis period. The induction period decreased and the lysis rate increased with increasing Cu(II) concentration. Cp or albumin, modified Cu(II) induced hemolysis, by increasing the duration of the induction period and decreasing the overall rate of hemolysis of RBC. The catastrophic lysis period coincided with a sharp increase in the formation of metHb within the cell and in a rapid uptake of Cu(II). The presence of Cp led to an increase in the induction period prior to the rapid increase in metHb formation and in Cu(II) uptake. Porcine Cp was prepared with either two or three nonprosthetic copper binding sites (sites where Cu(II) is easily removed by passing over Chelex-100). Cp with three nonprosthetic binding sites gave more protection than Cp with two. Likewise, albumin can be prepared with three and five nonprosthetic copper binding sites. The albumin with five sites gave more protection than the albumin with three sites.     

Biosynthesis of bacterial glycogen. Kinetic studies of a glucose-1-phosphate adenylyltransferase (EC 2.7.7.27) from a glycogen-deficient mutant of Escherichia coli B.

An Escherichia coli B mutant, SG14, accumulates glycogen at 28% the rate observed for the parent E. coli B strain. The glycogen accumulated in the mutant is similar to the glycogen isolated from the parent strain with respect to alpha- and beta-amylosis, chain length determination, and I2-complex absorption spectra. The SG14 mutant contains normal glycogen synthase and branching enzyme activity but has an ADP-glucose pyrophosphorylase with altered kinetic and allosteric properties. The mutant enzyme has been partially purified and requires a 12-fold higher concentration of fructose-P2 or a 26 fold higher concentration of pyridoxal-P than the parent type enzyme for 50% of maximal allosteric activation. TPNH, an effective activator of the E. coli B enzyme, does not activate the SG14 ADP-glucose pyrophosphorylase. Other studies show that for the SG14 enzyme the concentrations of ATP and Mg2+ in the synthesis direction and the concentrations of ADP-glucose and PPi in the pyrophosphorolysis direction required to give 50% of maximal activity are 3- to 6-fold higher than those observed for the parent E. coli B ADP-glucose pyrophosphorylase. The Km for alpha-glucose-1-P at saturating to half-saturating concentrations of the activator, fructose-P2, are about the same for both enzymes. However, in the presence of no activator, the concentration of glucose-1-P required for half-maximal activity is about 1.8-fold higher for the SG14 enzyme. Thus SG14 ADP-glucose pyrophosphorylase has lower affinity for its substrates than does the parent enzyme. Previously the SG14 enzyme had been shown to be less sensitive to inhibition by 5'-AMP than the E. coli B enzyme. This ensensitivity to inhibition renders the SG14 enzyme less responsive to energy charge than the E. coli B ADP-glucose pyrophosphorylase. On the basis of the above results and taking into account the reported concentrations of fructose-P2, of pyridoxal-P, and of the adenine nucleotide pool and its energy charge in E. coli strains, it is concluded that furctose-P2 is the important physiological allosteric activator of E. coli ADP-glucose pyrophosphorylase. Furthermore, the 1.7-fold increased rate of accumulation of glycogen observed when E. coli B or SG14 shifts from exponential phase to stationary phase of growth in nitrogen-limiting media can be accounted for by the 2.4-fold increase of the levels of the glycogen biosynthetic enzymes, glycogen synthase, and ADP-glucose pyrophosphorylase. Thus both allosteric regulation of the ADP-glucose pyrophosphorylase as well as the genetic regulation of the biosynthesis of the glycogen biosynthetic enzymes are involved in the regulation of glycogen accumulation in E. coli B.