Differential expression of excitatory amino acid receptor subtypes in cultured cerebellar neurons

Using neurotoxicity and inositol phosphate release as criteria for receptor expression, we report the differential expression of excitatory amino acid receptor subtypes in cerebellar granule cells grown in serum-free media containing either high (25 mM) or low (5 mM) KCl. NMDA receptors are expressed in neurons grown in high, but not low, KCl. In contrast, ionotropic quisqualate receptors are expressed in neurons grown in low KCl, but not in those grown in high KCl. Addition of NMDA to cultures containing low KCl appears to mimic high KCl conditions: NMDA receptors are expressed, but ionotropic quisqualate receptors are not. Glutamate and kainate are toxic to cells grown in either condition.

Calcium- and magnesium-binding properties of oncomodulin. Direct binding studies and microcalorimetry

Ca2+ binding to the wild type recombinant oncomodulin was studied by equilibrium flow dialysis in the absence and presence of 1, 2, and 10 mM Mg2+. Direct Mg2(+)-binding experiments were carried out by the Hummel-Dryer gel filtration technique. These studies revealed that in the absence of Mg2+ oncomodulin binds two Ca2+ with KCa = 2.2 x 10(7) and 1.7 x 10(6) M-1, respectively. In the absence of Ca2+ the protein binds only one Mg2+ with KMg = 4.0 x 10(3) M-1.Mg2+ antagonizes Ca2+ binding at the high affinity site according to the rule of direct competition. Ca2+ binding to the low affinity site is only slightly affected by Mg2+, so that in the presence of 2-3 mM Mg2+ the two sites have apparently an equal affinity for Ca2+. Microcalorimetry showed that, in spite of the different affinities of the two Ca2(+)-binding sites, delta H0 for the binding of each Ca2+ is identical and exothermic for -18.9 kJ/site. It follows that the entropy gain upon binding of Ca2+ is +77.1 J K-1 site-1 for the high affinity Ca2(+)-Mg2+ site and +56.0 J K-1 site-1 for the low affinity Ca2(+)-specific site. Mg2+ binding is endothermic for +13 kJ/site with an entropy change of +111 J K-1 site-1. The thermodynamic characteristics of the Ca2(+)-Mg2+ site resemble most those of site II (the so-called EF domain) of toad alpha-parvalbumin. The characteristics of Ca2+ binding to the specific site (likely the CD domain) are different from those of the Ca2+ specific sites in troponin C and in calmodulin and suggest that in oncomodulin hydrophobic forces do not play a predominant role in the binding process at the specific site.

Cardiac contusion in pediatric patients with blunt thoracic trauma

To investigate the prevalence of myocardial contusion associated with blunt chest trauma in the pediatric age group, all patients admitted to our institution during a 6-month period with blunt thoracic trauma severe enough to produce a pulmonary contusion or rib fracture were prospectively evaluated. Cardiac evaluation was undertaken, including a multiple-gated acquisition (MUGA) cardiac scan, serial electrocardiograms (ECG), and serum creatine phosphokinase (CPK) and CPK isoenzymes. Seven patients, ranging in age from 2 1/2 to 18 years, with rib fractures or pulmonary contusion by chest roentgenograph were identified. One patient was injured as a passenger in a motor vehicle accident, five were struck by automobiles as pedestrians, and one sustained traumatic asphyxia when a car, supported by a jack, fell on his chest. All had at least one other major organ system injured. All patients had pulmonary contusions as determined by chest radiograph, and two had associated rib fractures. In 43% (three of seven) of patients, a significant cardiac contusion was identified, defined by abnormal right or left ventricular wall motion and a decreased ejection fraction on MUGA scan, and confirmed by an increase in cardiac enzymes and isoenzymes. However, in contrast with adults, no patients had ECG abnormalities. This limited series suggests that cardiac contusion may occur frequently in pediatric patients who have suffered from blunt thoracic trauma significant enough to result in pulmonary contusion. An MUGA scan provides a rapid, noninvasive assessment of cardiac damage in this setting. Further studies will be required to determine the clinical significance and long-term consequences of traumatic myocardial damage in the pediatric population.

Neurotoxicity at the N-methyl-D-aspartate receptor in energy-compromised neurons. An hypothesis for cell death in aging and disease

Our results demonstrated that the neurotoxicity of glutamate and closely related agonists was mediated by the NMDA receptor in rat cerebellar granule cells. Evidence was presented to support our hypothesis that the pivotal event in the transition of these EAAs from neurotransmitters to neurotoxins is relief of the voltage-dependent Mg++ block of the NMDA channel due to changes in membrane potential which can be caused by depletion of highly phosphorylated nucleotides or by other depolarizing stimuli. Persistent stimulation of NMDA receptors whose channels are unblocked by Mg++ can permit excessive influx of Na+ and Ca++ and neuronal death can follow by a mechanism not yet understood. Glutamate is not toxic at kainate receptors although they are present on these cells. These findings underline the potential importance of perturbations in energy metabolism in a variety of neurodegenerative disorders and in the normal process of aging which share the common feature of the loss of neurons.

Excitatory amino acid neurotoxicity at the N-methyl-D-aspartate receptor in cultured neurons: pharmacological characterization

L-Glutamate neurotoxicity at the N-methyl-D-aspartate (NMDA) receptor was characterized in cultured cerebellar granule cells. When deprived of glucose for 40 min, these cells were killed by 20-60 microM L-glutamate. However, the neurons were resistant to glutamate at concentrations as high as 5 mM when glucose and Mg2+ were present throughout. Both competitive and non-competitive NMDA receptor antagonists completely blocked neurotoxicity due to glutamate and other NMDA receptor agonists. CPP [+/-)-3-(2-carboxypiperazin-4-yl)-prophyl-1-phosphonic acid) was the most effective competitive antagonist with full protection at 100 microM while MK-801 [+/-)-10,11-dihydro-5-methyl-5H-dibenzo[a,d]-cyclohepten-5,10-imin e) was the most effective non-competitive antagonist with full protection at 20 nM. Other antagonists with higher selectivity for other subtypes of glutamate receptors were ineffective. We conclude that glutamate toxicity in energy-deprived cerebellar granule cells is mediated by NMDA receptors. Results are discussed in terms of an hypothesis offering an explanation for the transition of glutamate from neurotransmitter to neurotoxin which emphasizes the responsiveness of the receptor to agonists rather than focusing on the presence of high concentrations of agonist.

Excitatory amino acid neurotoxicity at the N-methyl-D-aspartate receptor in cultured neurons: role of the voltage-dependent magnesium block

Results of the present report show that cerebellar neurons in primary culture are resistant to glutamate concentrations as high as 5 mM in the presence of glucose and Mg2+, but sensitive to glutamate concentrations lower than 35 microM when the neurons are deprived of glucose. Glutamate toxicity is also potentiated when Mg2+ is removed but glucose and EDTA are present; in this case, higher concentrations of glutamate (1 mM) are required for full toxicity. Glucose concentrations as low as 50 microM are fully protective against the toxicity of 100 microM glutamate; pyruvate and, to a lesser extent, lactate are also protective. Significantly, increasing concentrations of extracellular Mg2+ are fully protective against the toxicity of 100 microM glutamate in the absence of glucose and against the toxicity of 1 mM glutamate in the presence of glucose and EDTA. We interpret these results as support for our hypothesis that the pivotal event in glutamate's transition to neurotoxin is relief of the Mg2+ block of the N-methyl-D-aspartate (NMDA) receptor channel, which is known to be voltage-dependent. Partial depolarization in response to depletion of high-energy phosphates relieves the voltage-dependent block enabling glutamate to stimulate an excessive ion influx which results in the death of the neuron by a mechanism which is not yet understood. We propose that this mechanism may be operative in the neuronal damage associated with a variety of neurodegenerative disorders.

A new class of calcium entry blockers defined by 1,3-diphosphonates. Interactions of SR-7037 (belfosdil) with receptors for calcium channel ligands

Tetrabutyl-2(2-phenoxyethyl)-1,3-propylidene diphosphonate (SR-7037) completely displaced dihydropyridine [( 3H]PN200-110), phenylalkylamine [( 3H]D888), and benzothiazepine [( 3H]diltiazem) ligands from brain L-type calcium channels. Half-maximal inhibition of [3H]PN200-110 binding occurred at 19 nM with a Hill coefficient of 0.96. SR-7037 primarily decreased the affinity for [3H]PN200-110 with a small, but significantly, effect on the maximal binding capacity. Kinetic studies showed that this was due to an increased radioligand dissociation rate from 0.04 min-1 to 0.43 min-1 in the presence of the diphosphonate. Displacement of [3H]D888 by SR-7037 was biphasic with respective IC50 of 44 and 8400 nM. Likewise, unlabeled (-)-D888 identified two sites with IC50 values of 0.9 and 27 nM. Both SR-7037 (1000 nM) and D888 (200 nM) accelerated radioligand dissociation about 2-fold. [3H]Diltiazem binding was inhibited by SR-7037 with an IC50 value of 29 nM. The inhibition of dihydropyridine binding by SR-7037 is enhanced by most divalent cations at millimolar concentrations with the following potency: Mn2+ greater than Mg2+ greater than Ca2+ greater than Co2+. Barium has the opposite effect. The half-maximal effect of calcium occurred at 6 microM free ion. Specific binding of [3H]D888 was antagonized in the presence of 1 mM CaCl2. It is concluded that SR-7037 has allosteric interactions with the dihydropyridine receptor of the L-type calcium channel. The differential effect of Ca2+ on the potency of D888 and diltiazem relative to that of SR-7037 indicates that the three drugs may bind to nonequivalent sites. These results support specific calcium channel inhibition, possibly at a novel site, as the primary mechanism of the diphosphonate's pharmacological actions.

Voltammetric reduction and determination of hydrogen peroxide at an electrode modified with a film containing palladium and iridium

Cyclic voltammetry of a mixture containing 0.2 mM Na2IrCl6, 0.1 mM PdCl2, 0.2 M K2SO4, and 0.1 M HCl between 1.2 and -0.3 V vs Ag/AgCl for five cycles at 50 mV s-1 yields a stable film on a glassy carbon electrode. The reduction of hydrogen peroxide in 0.1 M KCl is diffusion controlled at that modified electrode. Calibration curves obtained at a 100 mV s-1 scan rate are linear in the range 0.2-1.8 mM H2O2. The slope, 28 microA L mmol-1, is independent of film thickness. Since dissolved oxygen is reduced at about the same potential as H2O2, -0.3 V, at the modified electrode, it will act as an interferent in solutions that are not deaerated; however, the currents are additive. A second limitation of the described procedure is that with the KCl electrolyte the immobilized film must be reoxidized prior to each measurement. Preliminary data are described which suggest that this problem is alleviated by switching to a basic supporting electrolyte.

Dynamic radionuclide imaging with 99mTc-sucralfate in the detection of oesophageal ulceration

Standard oesophageal scintigraphic techniques using 99mTc-colloids rarely identify oesophageal mucosal damage. Sucralfate can be labelled with 99mTc for the detection of oesophageal mucosal ulceration. This method uses two separate supine swallows of 10 MBq 99mTc-colloid in 10 ml, followed by a single supine swallow of 30 MBq 99mTc-sucralfate. The data are processed to give time-activity curves, mean transit times and condensed dynamic images. When oesophageal ulceration is detected, the time-activity curves using sucralfate show residual activity in the oesophagus after the transit time indicated by the colloid swallow. The condensed dynamic image shows a persistence of activity at the level of the ulceration. Erect sucralfate images taken immediately after the dynamic sequence show no oesophageal localisation. The results from a study of 62 patients have shown excellent correlation between the dynamic 99mTc-sucralfate images and endoscopy findings. Sequential sucralfate studies for healing also correlate well. The use of labelled sucralfate to detect oesophageal ulceration could modify the indications for endoscopy in gastrooesophageal reflux disease.

Mode of activation of bovine brain inositol 1,4,5-trisphosphate 3-kinase by calmodulin and calcium

The effect of Ca2+ and calmodulin (CaM) on the activation of purified bovine brain Ins(1,4,5)P3 kinase was quantified and interpreted according to the model of sequential equilibria generally used for other calmodulin-stimulated systems. Two main conclusions can be drawn. (i) CaM.Ca3 and CaM.Ca4 together are the biologically active species in vitro, as is the case for the great majority of other calmodulin targets. (ii) These species bind in a non-co-operative way to the enzyme with an affinity constant of 8.23 x 10(9) M-1, i.e. approx 10-fold higher than for most calmodulin-activated target enzymes. The dose-response curve of the activation of Ins(1,4,5)P3 kinase by calmodulin is not significantly impaired by melittin and trifluoperazine, whereas under very similar assay conditions the half-maximal activation of bovine brain cyclic AMP phosphodiesterase requires over 30-50-fold higher concentrations of CaM when 1 microM melittin or 20 microM-trifluoperazine is present in the assay medium. Similarly, 1 microM of the anti-calmodulin peptides seminalplasmin and gramicidin S, as well as 20 microM of N-(6-aminohexyl)-5-chloro-1-naphthalene-sulphonamide (W7), do not inhibit the activation process. These data suggest that binding and activation of Ins(1,4,5)P3 kinase require surface sites of calmodulin which are different from those involved in the binding of most other target enzymes or of model peptides.

Evidence for four capital and six auxiliary cation-binding sites on calmodulin: divalent cation interactions monitored by direct binding and microcalorimetry

Recently, Mills and Johnson [7] and our group [9] provided evidence that calmodulin contains, in addition to the four Ca2+-binding sites (capital sites), which are essential for drug- and enzyme-binding, a number of divalent cation-binding sites of different ion selectivity (auxiliary sites), which modulate drug-binding as well as the affinity of Ca2+ for the capital sites. In the present study, the number of auxiliary sites and their relationship to the capital sites were determined by equilibrium gel filtration and by flow microcalorimetry with Zn2+ and Mn2+ as selective probes for the auxiliary sites and with Cd2+ as a probe for both types of sites. In the absence of other divalent cations, 6 mol of Zn2+ bind to calmodulin with an identical affinity constant of 2,850 M-1 and a delta H0 of 106 kJ/mol calmodulin. In the presence of millimolar free Ca2+ calmodulin binds, in addition to four Ca2+, six Zn2+ with an affinity constant of 1,200 M-1 and a delta H0 of 47 kJ/mol calmodulin. The Zn2+-Ca2+ antagonism is governed by negative free energy coupling between the capital and auxiliary sites. In contrast, the Zn2+-Mg2+ antagonism follows the rule of straight competition at all six auxiliary sites. Mn2+ also binds exclusively to the auxiliary sites with affinity constants of 800 or 280 M-1 and delta H0 of 45 or 46 kJ/mol calmodulin in the absence and presence of saturating [Ca2+], respectively. Cd2+ binds to the capital sites with an affinity constant of 3.4 10(4) M-1 (delta H = 35 kJ/mol calmodulin) and to the auxiliary sites with ca. 100-fold lower affinity. The Zn2+ much greater than Mn2+ greater than or equal to Cd2+ greater than Mg2+ selectivity of the auxiliary sites corroborates the potencies of these cations in modulating drug binding. The auxiliary site-specific cations are unable to promote high-affinity complex formation between calmodulin and melittin.

Activation of human neutrophil NADPH-oxidase in vitro by the catalytic fragment of protein kinase-C

Phorbol ester treatment of intact neutrophils both stimulates protein kinase C (PK-C) and causes the rapid proteolytic conversion to a cytosolic, co-factor independent fragment, protein kinase M (PK-M). In intact neutrophils, phorbol ester treatment activates the NADPH-oxidase, the enzyme responsible for the oxidative burst. Addition of purified PK-M to resting neutrophil light density membranes activated the NADPH-oxidase in the presence of PS, ATP and Mg2+. A 3.5-fold greater stimulation of oxidase (ca. 25 nmoles O2-/min/mg membrane protein) was obtained with comparable PK-M concentrations to that observed with the reconstituted PK-C system, and approximately 1/3 that obtained with arachidonic acid (AA) or SDS. In contrast to the reconstituted system using PK-C, PMA and Ca++ were neither required nor affected activity. The effect of PS was unexpected, since PK-M does not require phospholipids for enzymatic activity, and likely represents the action of PS on the oxidase itself or on another component in the plasma membrane fraction. Our studies demonstrate for the first time that purified PK-M permits reconstitution of a physiologic phorbol ester response.

Complete amino acid sequence of the sarcoplasmic calcium-binding protein (SCP-I) from crayfish (Astacus leptodactylus)

The complete amino acid sequence of the alpha chain of the dimeric sarcoplasmic Ca2+-binding protein (SCP-I = alpha 2) from crayfish (Astacus leptodactylus) has been determined by partial automatic sequencing of the peptides derived from tryptic digests of the protein after citraconylation or treatment with 1,2-cyclohexanedione. Overlapping peptides were obtained by cleavage with o-iodosobenzoic acid, or digestion with Staphylococcus aureus protease, thermolysin and pepsin. The acetylated N-terminus was identified by fast atom bombardment mass spectrometry. The monomeric protein contains 192 amino acids and has an Mr of 21,643. The sequence shows the presence of three calcium-binding sites and perhaps of two others that may be degenerated.

Amino acid sequence of crayfish troponin I

Troponin I is the actomyosin ATPase inhibitory subunit present in the thin filament regulatory complex. The complete amino acid sequence of crayfish tail muscle troponin I has been determined. The protein is composed of 201 amino acid residues and has a molecular weight of 23,547. The N terminus is blocked, likely by an acetyl group. Crayfish troponin I shows a rather low (20-25%) sequence identity with vertebrate troponin Is as compared to the 60-82% identity within the vertebrate phylum. Similar to vertebrate cardiac troponin I, crayfish troponin I contains a 30-residue-long N-terminal extension. In crayfish troponin I, this segment bears significant sequence homology with the heavy or light chains of particular myosins. The actin-binding domain of crayfish troponin I, which displays 57% sequence homology with vertebrate troponin Is, possesses 2 unusual trimethyllysine residues. The consensus sequence of this domain in five troponin Is is as follows: D-L-R-G-K-F-X-R*-P-X-L-R*-R*-V, where R+ stands for Arg/Lys, R* for Arg/trimethyllysine, and X for any amino acid residue. Troponin I possesses two Ca2+-dependent interactive sites for troponin C; one partly overlaps with the actin binding domain and is highly conserved, and the other, corresponding to the 30-residue-long segment following the N-terminal extension in vertebrate cardiac and crayfish troponin I, is poorly conserved in the different troponin Is. Troponin I also interacts with troponin T. The consensus sequence for the interacting site on troponin I is as follows: h-D- -X-D- -R+-Y-D-h-E-h, where h stands for a hydrophobic residue, D- for Asp/Glu, R+ for Arg/Lys, and X for any residue. The five troponin Is further possess one more 15-residue-long segment of high sequence identity near the C terminus. Its evolutionary conservation suggests that this domain is involved in protein-protein interaction.

Amino acid sequence of a sarcoplasmic calcium-binding protein from the sandworm Nereis diversicolor

Muscles of invertebrate species contain abundant quantities of soluble, sarcoplasmic, high affinity Ca2+-binding proteins (SCBPs). The SCBPs belong to the calmodulin superfamily and contain four homologous domains (I-IV) which arose by reduplication of a gene for a small ancestral protein. We have determined the amino acid sequence of the SCBP from the sandworm Nereis diversicolor. This protein is the only SCBP which has been crystallized in a form suitable for three-dimensional structure determination by high-resolution x-ray analysis (Babu, Y. S., Cox, J. A., and Cook, W. J. (1987) J. Biol. Chem. 262, 11184-11185). N. diversicolor SCBP is a single polypeptide chain of 174 amino acids, including single residues of glutamine and histidine, 2 tyrosines, and 3 tryptophans. It is devoid of cysteine and has an acetylated amino terminus, a calculated Mr of 19,485, and a net charge of -13 at neutral pH. There was no evidence for heterogeneity in the sequence. Probable Ca2+-binding sites were recognized in domains I, III, and IV. Comparison with other available invertebrate SCBP sequences shows an unusually high degree of variability among these proteins, with only 9 residues common to all species.

Microcalorimetric investigation of the interaction of calmodulin with seminalplasmin and myosin light chain kinase

Flow microcalorimetric titrations of calmodulin with seminalplasmin at 25 degrees C revealed that the high affinity one-to-one complex in the presence of Ca2+ (Comte, M., Malnoe, A., and Cox, J. A. (1986) Biochem. J. 240, 567-573) is entirely enthalpy-driven (delta H0 = -50 kJ.mol-1; delta S0 = O J.K-1.mol-1; delta Cp0 = O J.K-1.mol-1) and is not influenced by the proton or Mg2+ concentration. The Sr2+- and Cd2+-promoted high affinity complexes are also exothermic for -49 and -45 kJ.mol-1, respectively. The observed low affinity interaction in the absence of divalent ions displays no enthalpy change. No enthalpy changes are observed when calmodulin and seminalplasmin are mixed in the presence of millimolar concentrations of Mg2+, Zn2+, or Mn2+. Enthalpy titrations of the 1:1 calmodulin-seminalplasmin complex with Ca2+ and of partly Ca2+-saturated calmodulin with seminalplasmin revealed that only the species calmodulin.Can greater than or equal to 2 is fully competent for high affinity interaction with seminalplasmin. Binding of the second Ca2+ is strongly enhanced (K2 greater than or equal to 5 X 10(7) M-1) as compared to that in free calmodulin (K2 = 2.6 X 10(5) M-1). This is essentially due to the concomitant strongly exothermic step of isomerization of the calmodulin-seminalplasmin complex from its low to its high affinity form. Binding of the remaining two Ca2+ to the high affinity seminalplasmin-calmodulin complex displays the same affinity constants and endothermic enthalpy change as in free calmodulin. A microcalorimetric study on the complex formation between Ca2+-saturated calmodulin and turkey gizzard myosin light chain kinase revealed that the interaction is strongly exothermic with an important overall gain of order (delta H0 = -85 kJ.mol-1; delta S0 = -122 J.K-1.mol-1) and occurs with significant proton uptake (0.44 H+ per mol at pH 7.5). The observed low affinity interaction (K = 2.2 X 10(5) M-1) in the absence of Ca2+ (Mamar-Bachi, A., and Cox, J. A. (1987) Cell Calcium 8, 473-482) displays neither a change in enthalpy nor in protonation.

Quantitative analysis of the free energy coupling in the system calmodulin, calcium, smooth muscle myosin light chain kinase

Interactions between Ca2+, calmodulin and turkey gizzard myosin light chain kinase have been studied by equilibrium gel filtration and analyzed in terms of the theory of free energy coupling as formulated by Huang and King for calmodulin-regulated systems (Current Topics in Cellular Regulation 27, 1966-1971, 1985). Direct binding studies revealed that upon interaction with the enzyme, calmodulin acquires strong positive cooperativity in Ca2+-binding. The determination of the Ca2+-binding constants is inherently approximative due to the apparent homotropic cooperativity; therefore a statistical chi 2 analysis was carried out to delimit the formation-, and subsequently the stoichiometric Ca2+-binding constants. Whereas the first two stoichiometric Ca2+-binding constants of enzyme-bound CaM do not differ or are at the upmost 10-fold higher than those in free calmodulin, the third Ca2+ ion binds with an at least 70-fold and more likely 3000-fold higher affinity constant. The binding constant for the fourth Ca2+ is only 5-fold higher than the corresponding one in free calmodulin, thus creating a plateau at 3 bound Ca2+ in the isotherm. Direct binding of Ca2+-free calmodulin to myosin light chain kinase at 10(-7) M free Ca2+ yielded a l/l stoichiometry and an affinity constant of 2.2 x 10(5) M-1. It is thus anticipated that in resting smooth muscle ([Ca2+] less than or equal to 10(-7) M) more than half of the enzyme is bound to metal-free calmodulin. Analysis of the enzymatic activation of myosin light chain kinase at different concentrations of calmodulin and Ca2+ revealed that this Ca2+-free complex is inactive and that activation is concomitant with the formation of the enzyme.calmodulin.Ca3 complex.

High-affinity formation of a 2:1 complex between gramicidin S and calmodulin

Two molecules of gramicidin S, a very rigid cyclic decapeptide rich in beta-sheet structure, can bind in a Ca2+-dependent way to a calmodulin molecule in the presence as well as in the absence of 4 M-urea. The flow-microcalorimetric titration of 25 microM-calmodulin with gramicidin S at 25 degrees C is endothermic for 21.3 kJ.mol-1; the enthalpy change is strictly linear up to a ratio of 2, indicating that the affinity constant for binding of the second gramicidin S is at least 10(7) M-1. In 4 M-urea the peptide quantitatively displaces seminalplasmin from calmodulin, as monitored by tryptophan fluorescence. An iterative data treatment of these competition experiments revealed strong positive co-operativity with K1 less than 5 X 10(5) M-1 and K1.K2 = 2.8 X 10(12) M-2. A competition assay with the use of immobilized melittin enabled us to monitor separately the binding of the second gramicidin S molecule: the K2 value is 1.9 X 10(7) M-1. By complementarity, the K1 value is 1.5 X 10(5) M-1. In the absence of urea the seminalplasmin displacement is incomplete: the data analysis shows optimal fitting with K1 less than 2 X 10(4) M-1 and K1.K2 = 3.2 X 10(11) M-2 and reveals that the mixed complex (calmodulin-seminalplasmin-gramicidin S) is quite stable and is even not fully displaced from calmodulin at high concentrations of gramicidin S. The activation of bovine brain phosphodiesterase by calmodulin is not impaired up to 0.2 microM-gramicidin S. According to our model the ternary complex enzyme-calmodulin-gramicidin is relatively important and displays the same activity as the binary complex enzyme-calmodulin. Gramicidin S also displaces melittin from calmodulin synergistically, as monitored by c.d. Our studies with gramicidin S reveal the importance of multipoint attachments in interactions involving calmodulin and confirm the heterotropic co-operativity in the binding of calmodulin antagonists first demonstrated by Johnson [(1983) Biochem. Biophys. Res. Commun. 112, 787-793].

Crystallization and preliminary x-ray investigation of sarcoplasmic calcium-binding protein from Nereis diversicolor

Crystals of sarcoplasmic calcium-binding proteins from Nereis diversicolor have been grown from solutions of ammonium sulfate. The crystals are monoclinic, space group P2(1); the axes are a = 43.65 (1), b = 56.05 (1), c = 65.77 (1) A, and beta = 92.58 (2) degrees. The crystals are quite stable to x-rays and diffract beyond 2.5 A resolution. The asymmetric unit contains two protein molecules.

Calcium-calmodulin stimulates inositol 1,4,5-trisphosphate kinase activity from insulin-secreting RINm5F cells

In a cytosolic fraction derived from insulin-secreting RINm5F cells, the rate of conversion of inositol 1,4,5-trisphosphate (Ins-1,4,5-P3) to inositol 1,3,4,5-tetrakisphosphate (Ins-1,3,4,5-P4) was half-maximally stimulated by 0.8 microM Ca2+ (Biden, T. J., and Wollheim, C. B. (1986) J. Biol. Chem. 261, 11931-11934). In the present study we show that after initial purification by anion exchange chromatography, the Ins-1,4,5-P3 kinase activity responsible for that conversion is stimulated by Ca2+-calmodulin, but not by Ca2+ alone. This is almost certainly due to a specific interaction of the enzyme and its activator since kinase activity was retained on a calmodulin-linked Sepharose 6B column in the presence of Ca2+ but eluted upon chelation of the cation. After this two-step purification, Ins-1,4,5-P3 kinase activity was maximally stimulated 5-fold by 10 microM calmodulin in the presence of 10(-5) M Ca2+, and 2 1/2-fold at 10(-6) M Ca2+. Under these conditions the minimum concentrations of calmodulin needed to stimulate activity were in the 10-50 nM range. At 10(-7) M Ca2+, calmodulin (up to 30 microM) was without effect. Stimulated Ins-1,4,5-P3 kinase activity was inhibited in a dose-dependent fashion by N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W7) although the calmodulin antagonist had no effect on the residual activity seen at 10(-7) M Ca2+. These results strongly support our previous suggestion that alterations in cytosolic free Ca2+ concentrations play an important role in regulating the levels of Ins-1,4,5-P3 and Ins-1,3,4,5-P4 during cellular stimulation.

Comparison of subcellular activation of the human neutrophil NADPH-oxidase by arachidonic acid, sodium dodecyl sulfate (SDS), and phorbol myristate acetate (PMA)

The phorbol myristate acetate (PMA) stimulation of the human neutrophil NADPH-oxidase has been demonstrated through the activation of protein kinase C (PK-C), using light membrane fractions from nitrogen-cavitated cells. Both arachidonic acid (AA) and sodium dodecyl sulfate (SDS) can also generate an active oxidase in cellfree systems. That the source of O2- with AA and SDS activation is the same NADPH-oxidase as previously studied was confirmed by the similar pH optima and Km values for NADPH as those previously described for the O2- -generating activity harvested from pre-stimulated human neutrophils. In contrast to the stimulation by PMA, however, the stimulation of the NADPH-oxidase by AA and SDS does not appear to require protein kinase C activation: the action of AA and SDS is independent of the addition of PK-C cofactors to the system, and the inhibitor of PK-C activity, H-7, had no effect on the stimulation by AA or SDS. AA and SDS activation are comparable, but the level of NADPH-oxidase expression is sixfold greater with each of these agents than that obtained with a reconstituted PK-C system. The basis of this difference in oxidase expression is unclear, but these findings suggest strongly that although activated PK-C is capable of stimulating a dormant NADPH-oxidase in a cellfree system, this is not the sole pathway for oxidase activation.

Comparison of subcellular activation of the human neutrophil NADPH-oxidase by arachidonic acid, sodium dodecyl sulfate (SDS), and phorbol myristate acetate (PMA)

The phorbol myristate acetate (PMA) stimulation of the human neutrophil NADPH-oxidase has been demonstrated through the activation of protein kinase C (PK-C), using light membrane fractions from nitrogen-cavitated cells. Both arachidonic acid (AA) and sodium dodecyl sulfate (SDS) can also generate an active oxidase in cellfree systems. That the source of O2- with AA and SDS activation is the same NADPH-oxidase as previously studied was confirmed by the similar pH optima and Km values for NADPH as those previously described for the O2- -generating activity harvested from pre-stimulated human neutrophils. In contrast to the stimulation by PMA, however, the stimulation of the NADPH-oxidase by AA and SDS does not appear to require protein kinase C activation: the action of AA and SDS is independent of the addition of PK-C cofactors to the system, and the inhibitor of PK-C activity, H-7, had no effect on the stimulation by AA or SDS. AA and SDS activation are comparable, but the level of NADPH-oxidase expression is sixfold greater with each of these agents than that obtained with a reconstituted PK-C system. The basis of this difference in oxidase expression is unclear, but these findings suggest strongly that although activated PK-C is capable of stimulating a dormant NADPH-oxidase in a cellfree system, this is not the sole pathway for oxidase activation.

The primary structure of a new Mr 18,000 calcium vector protein from amphioxus

The amino acid sequence of a new Ca2+-binding protein (CaVP) from Amphioxus muscle (Cox, J. A., J. Biol. Chem. 261, 13173-13178) has been determined. The protein contains 161 amino acid residues and has a molecular weight of 18,267. The N terminus is blocked by an acetyl group. The two functional Ca2+-binding sites have been localized based on homology with known Ca2+-binding domains, on internal homology and on secondary structure prediction, and appear to be the domains III and IV. The C-terminal half of CaVP, which contains the two Ca2+-binding sites, shows a remarkable similarity with human brain calmodulin (45%) and with rabbit skeletal troponin C (40%). Functional domain III contains 2 epsilon-N-trimethyllysine residues in the alpha-helices flanking the Ca2+-binding loop. Sequence determination revealed two abortive Ca2+-binding domains in the N-terminal half of CaVP with a similarity of 24 and 30% as compared with calmodulin and troponin C, respectively. This half is also characterized by the presence of a disulfide bridge linking the N-terminal helix of domain I to the C-terminal helix of domain II. This disulfide bond is very resistant to reduction in the native state, but not in denatured CaVP. The optically interesting aromatic chromophores (2 tryptophan and 1 tyrosine residues) are all located in the nonfunctional domain II.

Microcalorimetric investigation of the interactions in the ternary complex calmodulin-calcium-melittin

Flow microcalorimetric titrations of calmodulin with melittin at 25 degrees C revealed that the formation of the high-affinity one-to-one complex in the presence of Ca2+ (Comte, M., Maulet, Y., and Cox, J. A. (1983) Biochem, J. 209, 269-272) is entirely entropy driven (delta H0 = 30.3 kJ X mol-1; delta S0 = 275 J X K-1 X mol-1). Neither the proton nor the Mg2+ concentrations have any significant effect on the strength of the complex. In the absence of Ca2+, a nonspecific calmodulin-(melittin)n complex is formed; the latter is predominantly entropy driven, accompanied by a significant uptake of protons and fully antagonized by Mg2+. Enthalpy titrations of metal-free calmodulin with Ca2+ in the presence of an equimolar amount of melittin were carried out at pH 7.0 in two buffers of different protonation enthalpy. The enthalpy and proton release profiles indicate that: protons, absorbed by the nonspecific calmodulin-melittin complex, are released upon binding of the first Ca2+; Ca2+ binding to the high-affinity configuration of the calmodulin-melittin complex displays an affinity constant greater than or equal to 10(7) M-1, i.e. 2 orders of magnitude higher than that of free calmodulin; the latter is even more entropy driven (delta H0 = 7.2 kJ X site-1; delta S0 = 158 J X K-1 X site-1) than binding to free calmodulin (delta H0 = 4.7 kJ X site-1; delta S0 = 112 J X K-1 X site-1), thus underlining the importance of hydrophobic forces in the free energy coupling involved in the ternary complex.

Affinity purification of seminalplasmin and characterization of its interaction with calmodulin

Bull seminalplasmin antagonizes with high potency and selectivity the activating effect of calmodulin on target enzymes [Gietzen & Galla (1985) Biochem. J. 230, 277-280]. In the present paper we establish that seminalplasmin forms a 1:1, Ca2+-dependent and urea-resistant complex with calmodulin. The dissociation constant equals 1.6 nM. In the absence of Ca2+ a low-affinity complex is formed that is disrupted by 4 M-urea. On the basis of these properties, a fast affinity purification of seminalplasmin was developed. The high specificity of seminalplasmin as a calmodulin antagonist was demonstrated for the multipathway-regulated adenylate cyclase of bovine cerebellum. Far-u.v. c.d. properties are consistent with a random form of seminalplasmin in aqueous solution; 23% alpha-helix is induced on interaction with calmodulin. The fluorescence properties of the single tryptophan residue of seminalplasmin are markedly changed on formation of the complex. These studies allowed us to locate tentatively the peptide segment that interacts with calmodulin, and to ascertain the structural homology between seminalplasmin and other calmodulin-binding peptides. Additional material, showing the inhibition of calmodulin-mediated activation of bovine brain phosphodiesterase by melittin and seminalplasmin and also the near-u.v. spectrum of affinity-purified seminalplasmin, has been deposited as supplement SUP 50135 (4 pages) at the British Library Lending Division, Boston Spa, Wetherby, West Yorkshire LS23 7BQ, U.K., from whom copies may be obtained on the terms indicated in Biochem. J. (1986) 233, 5.

Calcium-proton and calcium-magnesium antagonisms in calmodulin: microcalorimetric and potentiometric analyses

Microcalorimetry, pH potentiometry, and direct binding studies by equilibrium dialysis or gel filtration were performed to determine the thermodynamic functions delta Ho, delta Go, and delta So guiding the interactions of Ca2+, Mg2+, and H+ with bovine brain calmodulin. At pH 7.5, Ca2+ and Mg2+ binding are both endothermic with enthalpy changes of 19.5 and 72.8 kJ X (mol of calmodulin)-1, respectively. These enthalpy changes are identical for each of the four ion-binding domains. The affinity constants also are identical with intrinsic values of 10(5) M-1 for Ca2+ and 140 M-1 for Mg2+. Ca2+ and Mg2+ do not compete for the same binding sites: at high concentrations of both ions, a calmodulin-Ca4-Mg4 species is formed with an enthalpy value of 24.4 kJ X mol-1 with respect to calmodulin-Ca4 and -28.8 kJ X mol-1 with respect to calmodulin-Mg4. Moreover, in the presence of high concentrations of Ca2+, the affinity of each of the four ion-binding domains in calmodulin for Mg2+ is decreased by a factor of 4 and vice versa, indicative of negative free-energy coupling between Ca2+ and Mg2+ binding. Protons antagonize Ca2+ and Mg2+ binding in a different manner. Ca2+-H+ antagonism is identical in each of the four Ca2+-binding domains in the pH range 7.5-5.2. Our analyses suggest that three chemical geometries, probably carboxyl-carboxylate interactions, are responsible for this antagonism with ionization constants of 10(6.2) M-1 in the metal-free protein. Mg2+-H+ antagonism also is identical for each of the Mg2+-binding sites but is qualitatively different from Ca2+-H+ antagonism.(ABSTRACT TRUNCATED AT 250 WORDS)

Isolation and characterization of a new Mr 18,000 protein with calcium vector properties in amphioxus muscle and identification of its endogenous target protein

A new Ca2+-binding protein, called CaVP, has been detected in muscle of the cephalochordate amphioxus and purified to electrophoretic homogeneity. The Mr 18,000 protein (pI = 4.9) binds 2 Ca2+ atoms in a noncooperative way with an intrinsic binding constant of 8.2 X 10(6) M-1. Ca2+, but not Mg2+, induces a 10% increase in alpha-helical content in the metal-free protein. CaVP does not interact with chlorpromazine, but forms a Ca2+-dependent complex with melittin. In situ, CaVP forms a high affinity Ca2+-dependent complex with an Mr 36,000 protein present in muscle extracts of amphioxus. This complex has been purified by gel filtration and ion exchange chromatography, and the target protein further purified after dissociation of the complex in the presence of Ca2+-chelating agents and 6 M urea. The nearly pure Mr 36,000 protein also forms a Ca2+-dependent complex with calmodulin which, however, is less stable during electrophoresis than the CaVP-Mr 36,000 protein complex. Amphioxus CaVP does not substitute for calmodulin in a specific enzyme assay nor for troponin C in restoring Ca2+ sensitivity to skinned muscle fibers. Its polyclonal antibody does not cross-react with the latter two activators. No immunological cross-reacting counterpart of CaVP was found in organs of fish and rat. Its relative abundance in amphioxus muscle indicates that CaVP must underlie an important new limb of Ca2+ regulation in this particular muscle.

Transtracheal repair of recurrent tracheoesophageal fistula

A recurrent tracheoesophageal fistula is generally associated with considerable mediastinal induration and inflammation. The conventional operative approach may be formidable with considerable blood loss and a high complication rate. For two infants with recurrent fistulae, we have employed a simplified low cervical transtracheal approach through noninflamed tissues. This brief atraumatic procedure was followed by gratifying results. Details of the approach are presented.

Calcium-calmodulin interaction and cellular function

Conformational and functional events in calmodulin (CaM) are directly governed by the degree of saturation by Ca2+, and do not depend on Ca2+-occupancy of any particular one of the four ion-binding sites. For instance, the exposure of a hydrophobicity at the surface of the protein coincides with the appearance of CaM X Can greater than or equal to 2. The species containing at least three Ca2+ is most often involved in target enzyme activation. The activation parameters explain the "on-off" behavior of the CaM-activated systems, in spite of the small amplitude of Ca2+-transients in stimulated cells. The strong energy coupling involved in activation is at the basis of a hysteretic behavior of the cell response: after the decay of free cytoplasmic Ca2+, the dissociation of the ternary complex between enzyme, CaM, and Ca2+ is delayed. Studying natural and synthetic model peptides that interact with CaM, we hope to obtain new insight into the CaM-binding domain in the different target enzymes. The minimal and sufficient requirement for high-affinity interaction of model peptides with CaM is a basic amphiphilic alpha-helix of at least 18 A. Preliminary data on the secondary structure of target enzymes indicate that their CaM-binding domains may have these structural requirements.

Activation of the human neutrophil nicotinamide adenine dinucleotide phosphate (NADPH)-oxidase by protein kinase C

A variety of phagocytosable and soluble agonists stimulate the human neutrophil respiratory burst enzyme, NADPH-oxidase, an activity required for normal microbicidal function. Of these agonists, the phorbol esters, which stimulate diverse systems by their ability to substitute for diacylglycerol to activate protein kinase C (the major phorbol ester receptor), have now been shown to directly stimulate NADPH-oxidase through this same receptor. Almost 90% of the specific receptors for phorbol 12,13-dibutyrate (PDBu) were found in the cytosol upon subcellular fractionation. The dissociation constant for [3H]PDBu was 1.2 nM. No significant difference was found in the distribution of the receptor between subcellular fractions from resting as compared with phorbol 12-myristate 13-acetate (PMA)-stimulated neutrophils. On the basis of these binding studies, we were able to establish a reconstituted system in which PMA activated dormant NADPH-oxidase in a light membrane fraction when cytosol, NADPH, phosphatidylserine, or phosphatidylinositol and ATP were added. The calcium chelator, EGTA, inhibited the activation, which suggested a requirement for calcium at low concentrations. The half-maximally effective PMA dose was 1.1 nM, as predicted from the receptor content in these preparations. Reconstitution of oxidase activity was rapid, peaking within 1 min of incubation. Purified protein kinase C was able to substitute for the cytosol fraction, and accounted for 80% of the cytosol activity. These studies demonstrate that phorbol esters stimulate the neutrophil respiratory burst through activation of cytosolic protein kinase C, which in turn activates either a regulatory constituent or the NADPH-oxidase directly in the plasma membrane to generate an active O-2-generating system.

Thermodynamics of the binding of calcium and strontium to bovine alpha-lactalbumin

Microcalorimetry and equilibrium gel filtration were used to determine the thermodynamic functions delta H degrees, delta G degrees and delta S degrees guiding the interaction of Ca2+ and Sr2+ with bovine alpha-lactalbumin. Two methods of nearly complete metal removal from the protein gave identical results. The single Ca- and Sr-binding site, which has moderate affinity for these ions (KCa = 2.5 X 10(6) M-1 and KSr = 5.1 X 10(5) M-1), displays unusually large enthalpy changes of -118 kJ X mol-1 for Ca2+ and -75 kJ X mol-1 for Sr2+. The concomitant reaction entropies equal -273 and -142 J X K-1 X mol-1, respectively.

Calcium-binding and its effect on circular dichroism of plant calmodulin

The Ca(2+)-binding properties of calmodulin purified from zucchini (Cucurbita pepo L.) has been determined. A value of 3.3 mol Ca(2+) per mol of zucchini calmodulin was measured at pH 7.5 by equilibrium chromatography. The far-and near-UV circular-dichroic spectra of the Ca(2+)-and Mg(2+)-saturated as well as from the metal-free forms of zucchini calmodulin reveal that upon Ca(2+)-binding the α-helix content increases. A comparison with the spectra of vertebrate calmodulin indicates that both calmodulin have a similar secondary structure, similar Ca(2+)-induced conformational changes and the same number of Ca(2+)-binding sites.

Relationship among calmodulin-, forskolin-, and guanine nucleotide-dependent adenylate cyclase activities in cerebellar membranes: studies by limited proteolysis

Adenylate cyclase activity in bovine cerebellar membranes is regulated by calmodulin, forskolin, and both stimulatory (Ns) and inhibitory (Ni) guanine nucleotide-binding components. The susceptibility of the enzyme to chymotrypsin proteolysis was used as a probe of structure-function relationships for these different regulatory pathways. Pretreatment of membranes with low concentrations of chymotrypsin (1-2 micrograms/ml) caused a three- to fourfold increase in basal adenylate cyclase activity and abolished the Ca2+-dependent activation of the enzyme by calmodulin. In contrast, the stimulation of the enzyme by GTP plus isoproterenol was strongly potentiated after protease treatment, an effect that mimics the synergistic activation of adenylate cyclase by Ns and calmodulin in unproteolyzed membranes. Limited proteolysis revealed low- and high-affinity components in the activation of adenylate cyclase by forskolin. The low-affinity component was readily lost on proteolysis, together with calmodulin stimulation of the enzyme. The activation via the high-affinity component was resistant to proteolysis and nonadditive with the Ns-mediated activation of the enzyme, suggesting that both effectors utilize a common pathway. The inhibitory effect of low concentrations (10(-7) M) of guanyl-5'-yl imidodiphosphate [Gpp(NH)p] on forskolin-activated adenylate cyclase was retained after limited proteolysis of the membranes, indicating that the proteolytic activation does not result from an impairment of the Ni subunit. Moreover, in the rat cerebellum, proteolysis as well as calmodulin was found to enhance strongly the inhibitory effect of Gpp(NH)p on basal adenylate cyclase activity. Our results suggest that calmodulin and Ns/Ni interact with two structurally distinct but allosterically linked domains of the enzyme. Both domains appear to be involved in the mode of action of forskolin.

Inguinal hernia of childhood

The early recognition and treatment of the inguinal hernia in childhood should result in negligible morbidity and mortality with current anesthetic and recovery room support. The outpatient management of the postoperative patient has contributed to this objective as well as reduced the overall cost.

The interaction of calmodulin with amphiphilic peptides

Calmodulin has recently been shown to form exceptionally tight, calcium-dependent complexes with several natural peptides (Kdiss greater than 10(-7) M). These peptides were demonstrated to be capable of forming basic, amphiphilic alpha-helices. To further illustrate the importance of this structural feature for calmodulin binding, several other amphiphilic alpha-helical peptides were tested for their ability to bind calmodulin. To monitor complexes of high affinity (greater than 10(8) M-1), a new competition assay was devised with Sepharose 4B-conjugated melittin. Stoichiometries were assessed by electrophoresis and equilibrium size exclusion chromatography. Three peptides, which were designed to form idealized amphiphilic alpha-helices were tested. The basic peptides, N alpha-9-fluorenylmethoxycarboxyl-(FMOC)-(Leu-Lys-Lys-Leu-Leu-Lys-L eu)1 and FMOC-(Leu-Lys-Lys-Leu-Leu-Lys-Leu)2 bind calmodulin in a 1:1 complex with dissociation constants of 150 and 3 nM, respectively. The acidic peptide, FMOC-(Leu-Glu-Glu-Leu-Leu-Glu-Leu)2 failed to bind calmodulin, even at micromolar concentrations. Complex formation between calmodulin and the 14-residue basic peptide leads to an increase in the helicity of the complex which is attributed to an increase of about 50% in the helicity of the peptide. Calmodulin also interacts with the neutral alpha-helical peptide toxin delta-hemolysin. Concomitant with binding, the fluorescence maximum of the unique Trp residue increases 2-fold and is blue-shifted. A dissociation constant could not be unambiguously estimated though, since delta-hemolysin has a strong tendency to self-aggregate. The above data support our hypothesis that a basic, amphiphilic alpha-helix is a structural feature which underlies the calmodulin-binding properties common to a variety of peptides.

The design, synthesis, and characterization of tight-binding inhibitors of calmodulin

Based on a consideration of the probable structure of calmodulin and some natural peptides known to interact with it, two calmodulin-binding peptides were designed. These peptides bind to calmodulin in helical conformations and are capable of forming electrostatic and hydrophobic interactions with calmodulin. Their dissociation constants for binding (less than or equal to 210 and 400 pM) place them as the tightest-binding inhibitors of calmodulin thus far reported. The study of the interactions of these and similar peptides with calmodulin will provide valuable insights into the mechanisms whereby calmodulin binds to target enzymes, and it also serves as an excellent model system for exploring the physical chemistry of protein-protein interaction.

Sequential events in calmodulin on binding with calcium and interaction with target enzymes

khe conformational and functional events in calmodulin (CaM) are disproportionate to the mean saturation by Ca2+. The enhancement of intrinsic tyrosine fluorescence closely follows the appearance of species CaM X Can greater than or equal to 1; the exposure of the hydrophobic patch at the surface of CaM coincides with the appearance of CaM X Can greater than or equal to 2. For the activation of four different target enzymes, i.e., brain phosphodiesterase and adenylate cyclase, red blood cell Ca,Mg-ATPase, and skeletal muscle phosphorylase b kinase, CaM X Can greater than or equal to 3 is required. The different enzymes have the same affinity for the active species. The direct interaction of CaM with Ca2+ and phosphorylase b kinase has been analyzed according to the theory of energy coupling: whereas the first two stoichiometric calcium-binding constants in the complex are not significantly different from those of free CaM, the third Ca2+ binds with an affinity at least 10(6)-fold higher to enzyme-bound CaM than to free CaM, which corresponds to a free energy coupling of -7 kcal/mol CaM. The similarities in the activation mechanism of different enzymes suggest the existence of one unique CaM-binding domain. The characteristics of the interaction between CaM and melittin, a small amphiphatic cytotoxin, led us to propose melittin as a model for such a CaM-binding domain.