Photosynthetic Carbon Metabolism in Photoautotrophic Cell Suspension Cultures Grown at Low and High CO(2)

Photosynthetic carbon metabolism was characterized in four photoautotrophic cell suspension cultures. There was no apparent difference between two soybean (Glycine max) and one cotton (Gossypium hirsutum) cell line which required 5% CO₂ for growth, and a unique cotton cell line that grows at ambient CO₂ (660 microliters per liter). Photosynthetic characteristics in all four lines were more like C₃ mesophyll leaf cells than the cell suspension cultures previously studied. The pattern of ¹⁴C-labeling reflected the high ratio of ribulosebisphosphate carboxylase to phosphoenolpyruvate carboxylase activity and showed that CO₂ fixation occurred primarily by the C₃ pathway. Photorespiration occurred at 330 microliters per liter CO₂, 21% O₂ as indicated by the synthesis of high levels of ¹⁴C-labeled glycine and serine in a pulse-chase experiment and by oxygen inhibition of CO₂ fixation. Short-term CO₂ fixation in the presence and absence of carbonic anhydrase showed CO₂, not HCO₃⁻, to be the main source of inorganic carbon taken up by the low CO₂-requiring cotton cells. The cells did not have a CO₂-concentrating mechanism as indicated by silicone oil centrifugation experiments. Carbonic anhydrase was absent in the low CO₂-requiring cotton cells, present in the high CO₂-requiring soybean cell lines, and absent in other high CO₂ cell lines examined. Thus, the presence of carbonic anhydrase is not an essential requirement for photoautotrophy in cell suspension cultures which grow at either high or low CO₂ concentrations.     

Role of Metabolites in the Reversible Light Activation of Pyruvate, Orthophosphate Dikinase in Zea mays Mesophyll Cells in Vivo

Whole leaf and mesophyll cell concentrations of pyruvate, phosphoenolpyruvate (PEP), ATP, and ADP were determined in Zea mays during the reversible light activation of pyruvate, orthophosphate dikinase in vivo. Mesophyll cell levels of the four metabolites were estimated by extrapolation from values in freeze-quenched leaf samples that were fractionated by differential filtration through nylon mesh nets (adapted from M Stitt, HW Heldt [1985] Planta 164: 179-188). During the 3 minutes required for complete light activation of dikinase, pyruvate levels in the mesophyll cell decreased (from 166 ± 15 to 64 ± 10 nanomoles per milligram of chlorophyll [nmol/mg Chl]) while PEP levels increased (from 31 ± 4 to 68 ± 4 nmol/mg Chl, with a transient burst of 133 ± 16 nmol/mg Chl at 1 minute). Mesophyll cell levels of ATP increased (from 22 ± 4 to 48 ± 3 nmol/mg Chl) and ADP levels decreased (from 16 ± 4 to 7 ± 6 nmol/mg Chl) during the first minute of illumination. Upon darkening of the leaf and inactivation of dikinase, pyruvate levels initially increased in the mesophyll (from 160 ± 30 to a maximum of 625 ± 40 nmol/mg Chl), and then slowly decreased to about the initial value in the light over an hour. PEP levels dropped (from 176 ± 5 to 47 ± 3 nmol/mg Chl) in the first 3 minutes and remained low for the remainder of the dark period. Mesophyll levels of ATP and ADP rapidly decreased and increased, respectively, about twofold upon darkening. The trends observed for these metabolite levels in the mesophyll cell during the light/dark regulation of pyruvate, orthophosphate dikinase activity suggest that pyruvate and PEP do not play a major role in vivo in regulating the extent of light activation (dephosphorylation) or dark inactivation (ADP-dependent threonyl phosphorylation) of dikinase by its bifunctional regulatory protein. While the changes in ADP levels appear qualitatively consistent with a regulatory role for this metabolite in the light activation and dark inactivation of dikinase, they are not of a sufficient magnitude to account completely for the tenfold change in enzyme activity observed in vivo.     

Phosphoserine as a recognition determinant for glycogen synthase kinase-3: phosphorylation of a synthetic peptide based on the G-component of protein phosphatase-1

Prior phosphorylation of its substrate has been shown to be important for substrate recognition by the protein kinase glycogen synthase kinase-3 (GSK-3). Phosphorylation of glycogen synthase by GSK-3 is known to be enhanced by the previous action of casein kinase II and the sequence -SXXXS(P)- was proposed as the minimal recognition determinant for GSK-3. The glycogen binding subunit of type 1 phosphoprotein phosphatase has been shown to be phosphorylated by cyclic AMP-dependent protein kinase at serine-13 in the sequence KPGFS(5)PQPS(9)RRGS(13)ESSEEVYV (F.B. Caudwell, A. Hiraga, and P. Cohen (1986) FEBS Lett. 194, 85-89). Inspection of the sequence revealed potential GSK-3 sites at residues 5 and 9. Using a synthetic peptide with the above sequence, we found that phosphorylation of serine-13 by cyclic AMP-dependent protein kinase permitted the recognition of serine-9 and serine-5 by GSK-3. The work provides another example of a substrate for GSK-3 and demonstrates that the action of GSK-3 is linked to the presence of phosphate in the substrate and not the action of any particular protein kinase. In the course of the analyses, a novel feature of trypsin cleavage of phosphopeptides was noted. In the sequence -SRRGS(P)- trypsin acted uniquely after the first arginine whereas in the sequence -S(P)RRGS(P)- it cleaved randomly at either arginine residue. The fact that GSK-3 could phosphorylate a peptide derived from a phosphatase subunit also raises the possibility that GSK-3 might be involved in controlling glycogen-associated type 1 phosphatase and, more generally, in mediating cyclic AMP control of protein phosphorylation in cells.     

Human responses to propionic acid. I. Quantification of within- and between-participant variation in perception by normosmics and anosmics

The objective of this study was to fully characterize normosmic perception of stimuli expected to cause widely varying degrees of olfactory and nasal trigeminal stimulation and to directly evaluate the possible role of olfactory nerve stimulation in nasal irritation sensitivity. During each of four identical test sessions, four anosmic and 31 normosmic participants were presented with a range of concentrations extending from peri-threshold for normosmics to supra- threshold for anosmics. For each session, odor (O) and nasal irritation (NI) sensitivities were summarized in terms of the concentrations required to produce four sensation levels ('iso-response' concentrations). Within-participant variation in these iso-response concentrations was < 10-fold for 95% of normosmics, for both O and NI. For O but not NI, these apparent fluctuations in sensitivity were largely accounted for by the uncertainty surrounding the iso-response concentrations calculated for each session. Anosmics exhibited minimal within- and between-participant variation in NI and required, for all but the highest perceptual level, a higher concentration than almost all normosmics. Between-participant variation, expressed in terms of 90% confidence interval widths, was approximately 0.5 log units for both O and NI for the highest perceptual level, but increased to approximately 0.8 and 1.8 log units, respectively, for the lowest (peri- threshold) level. Our findings suggest that: (i) most apparent variation over time in O sensitivity is actually a reflection of the uncertainty surrounding estimates of sensitivity obtained for each session; (ii) within- and between-participant variation in O sensitivity is far less than is commonly reported; and (iii) low to moderate levels of NI in normosmics are the result of relatively weak trigeminal stimulation combined with much greater olfactory activation.      

Monoclonal antibody 91.9H raised against sulfated mucins is specific for the 3'-sulfated Lewisa tetrasaccharide sequence

The IgG1hybridoma antibody, 91.9H, was originally raised against sulfated mucins isolated from normal human colonic mucosa. Previous studies have shown that the 91.9H antigen is expressed on normal colonic epithelial cells and the sulfomucins that they produce, but not in the normal small intestine and stomach. Tissue-specific changes occur in 91.9H antigen expression in disease: the antigen diminishes in colonic carcinomas, whereas in regions of gastric mucosa showing intestinal metaplasia and in gastric carcinomas, the antigen is expressed as a "neo-antigen." This report is concerned with elucidation, by the neoglycolipid technology, of the determinant recognized by antibody 91.9H using sulfated and sialyl oligosaccharides of Lewisa(Lea) and Lextypes, and analogs that lack sulfate, sialic acid, or fucose. Binding experiments with the lipid-linked oligosaccharides immobilized on chromatograms or on microwells, and inhibition of binding experiments with free oligosaccharides based on di-, tri- and tetrasaccharide backbones, show that the 91.9H antigenic determinant is based on a trisaccharide backbone, and consists of the 3'-sulfated Leatetrasaccharide sequence, which is a potent ligand for the E- and L-selectins. The antibody gives a relatively low signal with the 3'-sulfated non-fucosylated backbone, and has no detectable cross- reaction with the 3'-sulfated Lexisomer, nor with sialyl-Leaand - Lexanalogues. Antibody 91.9H is a valuable addition, therefore, to the repertoire of reagents for mapping details of the distribution, and determining the relative importance of sulfated and sialyl oligosaccharides as ligands for the selectins, in normal and pathological epithelia and endothelia.      

Light microscopic autoradiographic localization of [3H]pirenzepine and [3H](-)quinuclidinyl benzilate binding in human stellate ganglia

We have utilized the LKB Ultrofilm method of autoradiography to anatomically localize putative M1 and M2 muscarinic receptor subtypes in human stellate ganglia. Ten micron sections were labeled in vitro with either 1 nM of the classical antagonist [3H](-)quinuclidinyl benzilate ([3H](-)QNB) or 20 nM of the non-classical antagonist [3H]pirenzepine ([3H]PZ), using 1 microM atropine sulfate to define non-specific binding for both ligands. Our results indicate that [3H](-)QNB and [3H]PZ binding sites are distributed within the principal ganglion cells and nerve bundles.     

[3H] pirenzepine selectively identifies a high affinity population of muscarinic cholinergic receptors in the rat cerebral cortex

The specific binding of [³H] pirenzepine was investigated in homogenates of rat cerebral cortex, cerebellar cortex, and heart. Specific binding of [³H] pirenzepine in the cerebral cortex as defined by displacement with atropine sulfate (1μM) was of high affinity (K_d = 4–10 nM, receptor density = 1.06 pmoles/mg protein), stereoselective, and competitive with drugs specific for the muscarinic receptor. In contrast, few [³H] pirenzepine binding sites were demonstrated in cerebellar and heart homogenates.     

Muscarinic receptor binding in the mouse heart: the selective modulatory effect of fluoride ion on agonist binding

The effect of fluoride ion on the binding of the specific muscarinic agonist ligand [³H]c is methyldioxolane ([³H]CD) to the mouse cardiac muscarinic receptor was investigated. Utilizing equilibrium ligand binding experiments, sodium fluoride (10mM) was shown to decrease [³H]CD binding, measured at a concentration of 2 nM, by 52%. Studies with several different ions demonstrated that the reduction in [³H]CD binding was a specific effect of fluoride. This fluoride modulation was selective for agonist binding, as no effect of fluoride on the binding of the muscarinic antagonist [³H](?) quinuclidinyl benzilate (QNB) was observed.     

Maturation of mammalian myocardial muscarinic cholinergic receptors

Biochemical alterations of the cardiac muscarinic binding sites have not been correlated with physiological observations. The development of responsiveness to acetylcholine in the fetal mouse heart occurs during the third trimester. We tested the hypothesis that the altered physiological response was related to changes in the muscarinic cholinergic binding site assayed by using the potent antagonist [³H]-quinuclidinyl benzilate (QNB). Analysis of saturation isotherms of specific (atropine displaceable) [³H]-QNB binding gave an apparent dissociation constant (K_Dapp) of 27 ± 3 (SEM) pM for adult heart. Receptor density increased significantly during the third trimester of pregnancy to 48% of adult, while the K_Dapp did not change. The increase in receptor density parallels the demonstrated increased responsiveness to acetylcholine.     

Mediating delta-opioid-initiated heart protection via the beta2-adrenergic receptor: role of the intrinsic cardiac adrenergic cell

Stimulation of cardiac beta(2)-adrenergic receptor (beta(2)-AR) or delta-opioid receptor (DOR) exerts a similar degree of cardioprotection against myocardial ischemia in experimental models. We hypothesized that delta-opioid-initiated cardioprotection is mediated by the intrinsic cardiac adrenergic (ICA) cell via enhanced epinephrine release. Using immunohistochemical and in situ hybridization methods, we detected in situ tyrosine hydroxylase (TH) mRNA and TH immunoreactivity that was colocalized with DOR immunoreactivity in ICA cells in human and rat hearts. Western blot analysis detected DOR protein in ICA cells isolated from rat ventricular myocytes. The physiology of DOR expression was examined by determining changes of cytosolic Ca(2+) concentration ([Ca(2+)](i)) transients in isolated rat ICA cells using fluorescence spectrophotometry. Exposing the selective delta-opioid agonist D-[Pen(2,5)]enkephalin (DPDPE) to ICA cells increased [Ca(2+)](i) transients in a concentration-dependent manner. Such an effect was abolished by the Ca(2+) channel blocker nifedipine. HPLC-electrochemical detection demonstrated a 2.4-fold increase in epinephrine release from ICA cells following DPDPE application. The significance of the ICA cell and its epinephrine release in delta-opioid-initiated cardioprotection was demonstrated in the rat myocardial infarction model and ICA cell-ventricular myocyte coculture. DPDPE administered before coronary artery occlusion or simulated ischemia-reperfusion reduced left ventricular infarct size by 54 +/- 15% or myocyte death by 26 +/- 4%, respectively. beta(2)-AR blockade markedly attenuated delta-opioid-initiated infarct size-limiting effect and abolished delta-opioid-initiated myocyte survival protection in rat ICA cell-myocyte coculture. Furthermore, delta-opioid agonist exerted no myocyte survival protection in the absence of cocultured ICA cells during ischemia-reperfusion. We conclude that delta-opioid-initiated myocardial infarct size reduction is primarily mediated via endogenous epinephrine/beta(2)-AR signaling pathway as a result of ICA cell activation.