Covalent modification of human alpha-thrombin with pyridoxal 5'-phosphate. Effect of phosphopyridoxylation on the interaction of thrombin with heparin

Thermodynamic non-ideality as an alternative source of the effect of sucrose on the thrombin-catalyzed hydrolysis of peptide p-nitroanilide substrates

The inhibitory effect of sucrose on the kinetics of thrombin-catalyzed hydrolysis of the chromogenic substrate S-2238 (D-phenylalanyl-pipecolyl-arginoyl-p-nitroanilide) is re-examined as a possible consequence of thermodynamic non-ideality-an inhibition originally attributed to the increased viscosity of reaction mixtures. However, those published results may also be rationalized in terms of the suppression of a substrate-induced isomerization of thrombin to a slightly more expanded (or more asymmetric) transition state prior to the irreversible kinetic steps that lead to substrate hydrolysis. This reinterpretation of the kinetic results solely in terms of molecular crowding does not signify the lack of an effect of viscosity on any reaction step(s) subject to diffusion control. Instead, it highlights the need for development of analytical procedures that can accommodate the concomitant operation of thermodynamic non-ideality and viscosity effects.

A player of many parts: the spotlight falls on thrombin's structure

The wealth of structural information now available for thrombin, its precursors, its substrates, and its inhibitors allows a rationalization of its many roles. alpha-thrombin is a rather rigid molecule, binding to its target molecules with little conformational change. Comparison of alpha-thrombin with related trypsin-like serine proteinases reveals an unusually deep and narrow active site cleft, formed by loop insertions characteristic of thrombin. This canyon structure is one of the prime causes for the narrow specificity of thrombin. The observed modularity of thrombin allows a diversity in this specificity; its "mix-and-match" nature is exemplified by its interactions with macromolecules (Fig. 20). The apposition of the active site to a hydrophobic pocket (the apolar binding site) on one side and a basic patch (the fibrinogen recognition exosite) on the other allows for a fine tuning of enzymatic activity, as seen for fibrinogen. Thrombin receptor appears to use the same sites, but in a different way. Protein C seems only able to interact with thrombin if the recognition exosite is occupied by thrombomodulin. These two sites are also optimally used by hirudin, allowing the very tight binding observed; thrombin inhibition is effected by blocking access to the active site. On the other hand, antithrombin III makes little use of the recognition exosite; instead, its interactions are tightened with the help of heparin, which binds to a second basic site (the heparin binding site). Thrombin's modularity is a result of the conjunction of amino acid residues of like properties, such as charge or hydrophobicity. The charge distribution plays a role, not only in the binding of oppositely charged moieties of interacting molecules, but also in selection and preorientation of them. Nonproteolytic cellular properties are attributed to 1) the rigid insertion loop at Tyr60A, and 2) a partially inaccessible RGD sequence. The former can interact with cells in the native form; the latter would appear to be presented only in an (at least partially) unfolded state. The membrane binding properties of prothrombin can be understood from the ordered arrangement of calcium ions on binding to the Gla domain. Kringle F2 binds to thrombin at the heparin binding site through charge complementarity; a conformational change appears to occur on binding. The observed rigidity of the thrombin molecule in its complexes makes thrombin ideal for structure based drug design. Thrombin can be inhibited either at the active site or at the fibrinogen recognition exosite, or both.(ABSTRACT TRUNCATED AT 400 WORDS)

Linkage between proton binding and amidase activity in human gamma-thrombin

The amidase activity of human gamma-thrombin has been studied in the pH range 6-10 as a function of NaCl concentration and temperature. As recently found for human alpha-thrombin [Di Cera, E., De Cristofaro, R., Albright, D.J., & Fenton, J.W., II (1991) Biochemistry 30, 7913-7924], the Michaelis-Menten constant, Km, shows a bell-shaped dependence over this pH range with a minimum around pH 7.9 in the presence of 0.1 M NaCl at 25 degrees C. The catalytic constant, kcat, has a bell-shaped pH dependence with a maximum around pH 8.6. A thermodynamic analysis of these parameters has enabled a characterization of the linkage between proton and substrate binding, its dependence on NaCl concentration, and the relevant entropic and enthalpic contributions to binding and catalytic events. Three groups seem to be responsible for the control of gamma-thrombin amidase activity as a function of pH. One of these groups has pK values that are significantly different from those found for alpha-thrombin, and all groups show slightly perturbed enthalpies of ionization. The dependence of gamma-thrombin amidase activity on NaCl concentration is different from that of alpha-thrombin. Increasing NaCl concentration always decreases the substrate affinity for the enzyme in the case of alpha-thrombin, regardless of pH. In the case of gamma-thrombin, such an effect is observed only in the pH range 7.5-9, and a reversed linkage is observed at pH less than 7 and greater than 9.5.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of thrombin-fibrinogen interaction by specific ion effects

Steady-state measurements of synthetic substrate hydrolysis by human alpha-thrombin in the presence of human fibrinogen, under experimental conditions where light scattering due to the formation of fibrin aggregates is negligible, have allowed for a quantitative evaluation of Km for fibrinogen. Measurements of Km for fibrinogen carried out at pH 7.5 and 37 degrees C as a function of NaCl, NaBr, KCl, and KBr concentration, from 50 to 500 mM, show that the derivative d ln Km/d ln a +/-, where a +/- is the mean ion activity, is constant over the entire range of salt concentrations and is strictly dependent on the particular salt present in solution. The values of d ln Km/d ln a +/- are found to be equal to 0.75 +/- 0.03 (NaCl), 0.90 +/- 0.01 (NaBr), 0.62 +/- 0.07 (KCl), and 0.60 +/- 0.03 (KBr). Measurements of Km for two synthetic amide substrates, under identical solution conditions, reveal practically no change in Km with salt concentration, while they show a significant decrease in kcat when Na+ salts are replaced by K+ salts. The drastic difference in the salt dependence of Km between fibrinogen and the synthetic amide substrate points out that a significant role may be played by the fibrinogen recognition site in the energetics of thrombin-fibrinogen interaction. The sensitivity of Km for fibrinogen to different salts unequivocally demonstrates that specific ion effects, rather than nonspecific ionic strength effects, modulate thrombin-fibrinogen interaction under experimental conditions of physiological relevance. Analysis of ion effects on clotting curves obtained at pH 7.5 and 37 degrees C also shows a drastic differential effect of cations and anions.(ABSTRACT TRUNCATED AT 250 WORDS)

Linkage between proton binding and amidase activity in human alpha-thrombin: effect of ions and temperature

The amidase activity of human alpha-thrombin has been studied at steady state in the pH range 6-10, as a function of NaCl concentration from 1 mM to 1 M and temperature from 10 to 40 degrees C. The Michaelis-Menten constant, Km, shows a bell-shaped dependence over this pH range with a minimum around pH 7.5 in the presence of 0.1 M NaCl at 25 degrees C. The catalytic constant, kcat, also has a bell-shaped pH dependence with multiple inflection points that are more evident at low NaCl concentrations and a maximum around pH 8.2 in the presence of 0.1 M NaCl at 25 degrees C. A detailed analysis of the results in terms of a general linkage scheme has allowed a thorough characterization of the linkage between proton and substrate binding and its dependence on NaCl concentration, as well as the relevant entropic and enthalpic contributions to binding and catalytic events. Formulation of detailed partition functions for each enzyme intermediate involved in the catalytic cycle suggests that (at least) three groups are responsible for the control of thrombin amidase activity as a function of pH. One group is to be identified with the active site His, due to its pK values in the free enzyme and the adduct and its enthalpy of ionization. The effect of NaCl concentration on amidase activity seems to be extremely specific. Comparative steady-state measurements carried out in the presence of NaCl, NaBr, NaI, KCl, and MgCl2 show that human alpha-thrombin is capable of discriminating among different cations and anions. This suggests that small ions participate as allosteric effectors in the regulation of thrombin activity. The linkage with NaCl is strongly pH dependent and increases with decreasing pH. The present results provide information on the basic aspects of human alpha-thrombin activity and regulation and enable a rigorous thermodynamic approach to other important regulatory interactions in human alpha-thrombin and its structurally perturbed derivatives.

The use of acetylated factor X to prevent feedback activation of factor VIII during factor X activation: a tool for kinetic studies

The modification of human factor X by 2-sulfo-N-succinimidyl acetate was investigated and shown to produce a factor X species which, when activated, has no activity toward factor VIII. Acylation of factor X (0.9 microM) was carried out in the presence of 1 mM calcium at different reagent concentrations and pH values at 22 degrees C for time courses up to 1 h. Optimal modification was achieved using 0.3 mM reagent at pH 8.0 for 30 min. The modified zymogen, acetylated factor X, is activated at full rates by factor IXa/VIIIa and by the factor X-activating protein of Russell's viper venom. The activated product, acetylated Xa, has an enhanced amidolytic activity (110%) but has almost no detectable clotting activity (0.1%). More importantly, we have shown that acetylated Xa, in contrast to native Xa, does not activate factor VIII. This allows accurate quantitation of factor VIII activation without complications due to positive feedback reactions. We have demonstrated this in an examination of the activation of factor VIII by factor IXa.

The heparin and pentosan polysulfate binding sites of human antithrombin overlap but are not identical

Four sulfated polysaccharides (unfractioned heparin, low-molecular-mass heparin, heparan sulfate and pentosan polysulfate) were investigated for their abilities (a) to bind antithrombin, (b) to induce conformational change of the inhibitor and (c) to potentiate antithrombin inhibition of thrombin. The binding capacity was reflected by the shielding of the heparin binding site. This was characterized by the extent to which a polysaccharide could protect chemical modification of Lys-125 and Lys-136, two lysyl residues of antithrombin which have been implicated in heparin binding. The conformational change was measured by fluorescence enhancement and the increased accessibility of Lys-236 to chemical modification. Our results reveal that the events of polysaccharide binding, conformational change and the enhancement of inhibitory activity are not quantitatively interlinked. Compared to the unfractionated heparin on an equal mass basis, the low-molecular-mass heparin (molecular mass 4-6 kDa) binds more strongly to antithrombin, induces a greater conformational change (about twofold), but is less potent in accelerating the inhibitory activity. Both heparin and heparan sulfate shield Lys-125 and Lys-136 and induce a conformational change that leads to exposure of Lys-236 and an increased fluorescence. On the other hand, pentosan polysulfate protects only Lys-125 and causes no appreciable conformational change, although it is also capable of enhancing the antithrombin-thrombin interaction. These data clearly demonstrate that the heparin and pentosan polysulfate binding sites of antithrombin overlap (at Lys-125) but are not identical.

Identification of the primary structural defect in the dysthrombin thrombin Quick I: substitution of cysteine for arginine-382

A congenitally dysfunctional form of prothrombin, prothrombin Quick, was isolated from the plasma of an individual with less than 2% of normal prothrombin activity. Following activation of prothrombin Quick, two dysfunctional thrombins, thrombin Quick I and thrombin Quick II, were isolated. Functional characterization of thrombin Quick I indicated an increase in KM and a decrease in kcat, relative to thrombin, for release of fibrinopeptide A. Comparison of kcat/KM for thrombin Quick I to the value obtained for thrombin yielded a relative catalytic efficiency of 0.012 for thrombin Quick I [Henriksen, R. A., & Owen, W. G. (1987) J. Biol. Chem. 262, 4664-4669]. Lysyl endopeptidase digestor of reduced and S-carboxymethylated thrombin and thrombin Quick I has resulted in the identification of an altered peptide in this dysthrombin. Edman degradation of the isolated peptide has shown that the altered residue in this protein is Arg-382 which is replaced by Cys. This could result from a point mutation in the Arg codon, CGC, to yield TGC. Together, these results indicate that Arg-382 is a critical residue in determining the specificity of thrombin toward fibrinogen. Similar relative activities for thrombin Quick I in stimulating platelet aggregation, in the release of prostacyclin from human umbilical vein endothelium, and in the release of fibrinopeptide A suggest that these activities of thrombin share the same specificity determinants.

Binding of heparin or dermatan sulfate to thrombin is essential for the sulfated polysaccharide-accelerated inhibition of thrombin by heparin cofactor II

Heparin cofactor II (HC II) and thrombin were chemically modified with pyridoxal 5'-phosphate, and their effects on the inhibition of thrombin by HC II in the presence of heparin or dermatan sulfate were studied. The inhibition of thrombin by HC II was enhanced about 7000-fold in the presence of heparin or dermatan sulfate. However, this enhancement by heparin dwindled to 110- and 9.6-fold when the modified HC II and the modified thrombin, respectively, were substituted for native proteins. Essentially identical results were obtained from the experiments using dermatan sulfate. These results indicate that the binding of heparin or dermatan sulfate to both thrombin and HC II is required for the sulfated polysaccharide-dependent acceleration of the thrombin inhibition by HC II, and the binding to thrombin is more essential for the reaction.

Effect of limited modification of amino groups on the reactivity of human factor Xa

The basis of the specificity of human coagulation factor Xa has been probed with a reagent that reacts with nucleophiles, N-succinimidylpropionate. At pH 8.0 and 0.25 mM N-succinimidylpropionate, 0.4 microM factor Xa lost approx. 90% of its activity toward prothrombin in 4 min. The decay was first-order, k = 0.64 min-1, which increased to 0.98 min-1 in 1 mM Ca2+, and the dependence of k upon pH was consistent with primary amines being the target. The rate of modification was unaffected by the presence of a tetrapeptide substrate during modification; likewise, activity toward a tripeptide p-nitroanilide was unaltered during exposure of factor Xa to N-succinimidylpropionate with or without Ca2+. In addition, inhibition by antithrombin III was retained with a somewhat enhanced rate after modification; however, the acceleration of this by heparin was significantly less. Kinetic determination of the number of residues modified gave a reaction order of 2.0, while reaction with N-succinimidyl[3H]propionate yielded labeled factor Xa containing 1.0 mol N-succinimidylpropionate/mol factor Xa and 50% normal clotting activity, or 2.0 mol N-succinimidylpropionate/mol and 1% activity, respectively. Thus, one nucleophilic group is required for the reaction of factor Xa with prothrombin but not for the hydrolysis of peptides or recognition of antithrombin III. The decay of clotting activity of the factor X zymogen in N-succinimidylpropionate was much slower though still Ca2+-dependent. Conversely, the reaction of a related compound--N-succinimidyl(4-hydroxyphenyl)propionate or Bolton-Hunter reagent--with factor Xa broadly resembled that of N-succinimidylpropionate but the decay curves indicated more complex kinetics. Therefore, the target groups vary in their accessibility to modification according to the structural characteristics of both the protein and the reagent.

The anticoagulant properties of mast cell product, chondroitin sulphate E

The anticoagulant potency in vitro of chondroitin sulphate E has been found to be similar to that of the heparinoids. In purified systems chondroitin sulphate E was shown to be principally an activator of heparin cofactor II. Maximum acceleration of heparin cofactor II:thrombin interaction was 185-fold (9.3 X 10(7) M-1 min-1), antithrombin III:thrombin interaction was 11-fold (4.16 X 10(6) M-1 min-1) and antithrombin III:factor Xa was 146-fold (3.86 X 10(6) M-1 min-1). Chondroitin sulphate E was observed to prolong the thrombin clotting time of fibrinogen in the absence of antithrombin III and heparin cofactor II. The effect appeared to be related to interference in thrombin:fibrinogen interaction rather than in fibrin monomer polymerization.

Catalytic and regulatory functions of N-bromosuccinimide-modified bovine thrombin

At pH 4.1, bovine thrombin reacts rapidly with N-bromo-succinimide to yield modified enzyme containing oxidized tryptophan residue. Both fibrinogen clotting activity and esterase activity are reduced considerably when three moles of tryptophan residues per mole of thrombin are oxidized, but the Michaelis constants for synthetic substrates are not appreciably altered. Reaction of NBS also results in a decrease in the affinity of thrombin for heparin. The dissociation constant for heparin-thrombin complex is increased by 2.6-fold due to the modification of one tryptophan residue. However, the magnitude of the increase in the dissociation constant remains the same for modified enzymes containing approximately two or three oxidized tryptophan residues. The rate constant for the inactivation of thrombin by antithrombin III is increased by 2.5-fold due to the modification of a single tryptophan residue. This increase in rate constant is not further amplified when more than one tryptophan residue is oxidized. In contrast, in the presence of heparin the rate of inactivation of modified and unmodified thrombins by antithrombin III are not significantly different. Thus, the heparin-sensitized inactivation of thrombin by antithrombin III is affected by the modification of one tryptophan residue. Spectrophotometric titrations of the phenolic hydroxyl groups suggest that the structural environments of tyrosyl groups for both unmodified and modified thrombin containing one oxidized tryptophan residue, are similar. The temperature for half loss of catalytic activity of control and NBS-modified thrombin, containing one oxidized tryptophan, are 52 and 51.5 degrees C respectively. It appears that the one tryptophan residue of thrombin is situated at or close to the binding site of heparin.

Origin of a fluorescence increase accompanying the limited proteolysis of fluorescein-labeled human prothrombin by Factor Xa

In a search for a probe which would report its proteolysis to thrombin, the human blood coagulation zymogen prothrombin was covalently labeled with fluorescein. Fluorescein isothiocyanate (FITC) and dichlorotriazinylaminofluorescein (DCTAF) both introduced approximately 1 molecule of dye, but labeling occurred at different locations, as FITC had no effect on clotting activity whereas DCTAF caused 95% inactivation. At pH 9.0 DCTAF, but not FITC, could induce labeling up to 4 mol/mol. All derivatives were activated normally by prothrombinase (the activating complex of Factor Xa, Factor V(a), Ca2+ and phospholipids), as indicated by the pattern of bands on SDS gel electrophoresis and an unaltered yield of activity toward a chromogenic substrate for thrombin. Upon undergoing this limited proteolysis, the most heavily labeled derivative showed a 40% increase in fluorescence of the fluorescein at 520 nm (lambda ex 480 nm). In contrast, the fluorescence of lightly labeled forms was more intense but increased by only 0-5% upon activation. The data suggest that the lower fluorescence of the most labeled form is due to an intramolecular quenching effect between the dye molecules on individual polypeptide chains that is partly relieved when activation occurs.

A general immunochemical method for detecting proteins on blots

Following horizontal electroelution, or blotting, of proteins from polyacrylamide gels to immobilizing matrices, such as nitrocellulose or Zeta-bind paper, the transferred proteins can be derivatized in situ with pyridoxal 5'-phosphate and sodium borohydride. After a quenching step to eliminate nonspecific binding of antibody to the protein-binding matrix, the blot is incubated with a solution containing a mouse monoclonal antibody specific for the 5'-phosphopyridoxyl group. The transferred proteins can then be located on the blot with second antibody staining procedures employing either a peroxidase-linked goat anti-mouse F(ab')2 antibody or a peroxidase-linked avidin/biotin system. The solid-phase enzyme-linked immunosorbent assay method described in this report is a mild, general, and sensitive immunochemical method for the detection of proteins on protein-binding matrices.

Selective inhibition of thrombin by (2R,4R)-4-methyl-1-[N2-[(3-methyl-1,2,3,4-tetrahydro-8-quinolinyl++ +) sulfonyl]-l-arginyl)]-2-piperidinecarboxylic acid

The potency of thrombin inhibition by 4-methyl-1-[N2-[(3-methyl-1,2,3,4-tetrahydro-8-quinolinyl)-sulfony l]- L-arginyl]-2-piperidinecarboxylic acid (MQPA) depended on the stereoconformation of the 2-piperidinecarboxylic acid moiety. Ki values for bovine alpha-thrombin were 0.019 microM with (2R,4R)-MQPA, 0.24 microM with (2R,4S)-MQPA, 1.9 microM with (2S,4R)-MQPA, and 280 microM with (2S,4S)-MQPA. (2R,4R)-MQPA of the four stereoisomers of MQPA was also the most potent inhibitor for other trypsin-like serine proteases with Ki values of 5.0 microM for trypsin, 210 microM for factor Xa, 800 microM for plasmin, and 1500 microM for plasma kallikrein. Examination of the potency of thrombin inhibition by arginine derivatives related to MQPA in structure suggested the presence of a specific binding site for the carboxamide portion (C-terminal side). The relative inhibitory potency of the four stereoisomers of MQPA for trypsin was nearly identical with that for thrombin, suggesting that the specific binding site for the carboxamide portion is present in both enzymes. Modification of thrombin by phosphopyridoxylation or the presence of heparin did not significantly alter the binding of MQPA.

Modulatory effects on proteinase kinetics caused by association of both enzyme and substrate to heparin

Heparin is shown to produce modulatory effects on the amidolytic activity of trypsin, thrombin and plasmin with various synthetic peptide substrates. Simple Michaelis-Menten kinetics are observed in the absence of heparin. In its presence an enhancement effect is observed at low substrate concentrations, and an inhibitory effect is observed at high substrate concentrations. Other polyanions like dextran sulphate, phosvitin and inositol hexakisphosphate produces a similar effect. The modulatory effect of heparin is abolished when it binds cations. Co-binding of both substrate and enzyme to heparin seems to be a necessary requirement for the effect to occur. A model is proposed which can account semiquantitatively for the kinetics observed. It is suggested that the mechanism, which involves co-binding of substrate and enzyme in an competitive manner to a macromolecular structure, may be of primary importance as a regulatory mechanism in blood coagulation and fibrinolysis.

Enzymic activity of thrombin with partially reduced disulfide bonds

Partial reduction of thrombin disulfide bridges with dithiothreitol in the absence of denaturants inhibits the fibrinogen clotting but not the esterase activity of the enzyme. The clotting activity reappears on spontaneous air reoxidation of thrombin. As a result of the reaction with dithiothreitol, two disulfide bonds are cleaved in thrombin molecule inducing a small decrease of beta-sheets in the secondary structure of thrombin. It may be concluded that this modification does not affect the catalytic site of thrombin but has influence upon the fibrinogen binding (recognition) site.

Calcium inhibits the heparin-catalyzed antithrombin III/thrombin reaction by decreasing the apparent binding affinity of heparin for thrombin

The present study has shown that calcium inhibits the heparin-catalyzed antithrombin III/thrombin reaction. The initial rate of thrombin (4.0 nM) inhibition by antithrombin III (200 nM) in the presence of heparin (2.5 ng/ml) decreased from 3.6 nM/min (in the absence of calcium) to 0.12 nM/min in the presence of 10 mM calcium. In the absence of heparin, the initial rate of thrombin inhibition by antithrombin III was not affected by calcium. The heparin-catalyzed antithrombin III/thrombin reaction is described by the general rate equation for a random-order, bireactant, enzyme-catalyzed reaction (M. J. Griffith (1982) J. Biol. Chem. 257, 13899-13902). As such, the reaction is saturable with respect to both thrombin and antithrombin III. The apparent kinetic parameters for the heparin-catalyzed antithrombin III/thrombin reaction were determined in the presence and absence of calcium. The apparent heparin/antithrombin III dissociation constant values were not measurably different in the presence of 0, 1.0, and 3.0 mM calcium. The apparent heparin/thrombin dissociation constant value increased from 7.0 nM, in the absence of calcium, to 10 and 30 nM in the presence of 1.0 and 3.0 mM calcium, respectively. The maximum reaction velocity, at saturation with respect to both proteins, was not affected by calcium. It is concluded that calcium binds to functional groups within the heparin molecule which are required for thrombin binding.

Post-translational carboxylation of preprothrombin

In summary, in this review on the function of vitamin K in post-translational modification of precursor proteins by carboxylation of certain glutamyl residues, I have tried to cover in particular the recent work on the reaction, the enzymes involved and the mechanisms being considered. In doing this I have also considered vitamin K, its discovery, its functional form and the possible relation of its metabolism to the carboxylation reaction. Equally the various vitamin K-dependent gla-containing proteins currently known have been described. The carboxylation of synthetic small molecule exogenous substrates and the synthesis and metabolism of the products of carboxylation are of great help in studying the reaction. Structural specificity of vitamin K analogs in vivo and in vitro has been compared and the use of various antagonists in vivo and in vitro considered in attempts to gain an understanding of the overall reaction. The reactions subsequent to carboxylation, e.g., the activation of prothrombin to thrombin via serine proteases and the related activation of the other vitamin K-dependent proteins have not been considered in this review. The review has not covered prothrombin or other vitamin K-dependent protein isolation, nor the determination of these proteins. As the vitamin K-dependent protein carboxylation story has developed over the past six years, a number of reviews have been written which help in keeping up with the various aspects of the field as it has expanded. These reviews refer to many of the papers I have had to eliminate due to space limitations. They are referenced as 469-489. The review is in no sense comprehensive and many papers have been missed or only mentioned. I have tried to concentrate on the more recent work and, thus, much of the very fine work of the 1940's on vitamin K chemistry is hardly mentioned. Some redundancy has been built into the organization of the review so that a reader can obtain a reasonable view of any one section without having to search the whole review for all possible relevant information on any particular part of the field.