The reaction of rabbit muscle creatine kinase with some derivatives of iodoacetamide

Alkylation of rabbit muscle creatine kinase surface methionine residues inhibits enzyme activity in vitro

Creatine kinase (CK) catalyzes the formation of phosphocreatine from adenosine triphosphate (ATP) and creatine. The highly reactive free cysteine residue in the active site of the enzyme (Cys²⁸³) is considered essential for the enzymatic activity. In previous studies we demonstrated that Cys²⁸³ is targeted by the alkylating chemical warfare agent sulfur mustard (SM) yielding a thioether with a hydroxyethylthioethyl (HETE)-moiety. In the present study, the effect of SM on rabbit muscle CK (rmCK) activity was investigated with special focus on the alkylation of Cys²⁸³ and of reactive methionine (Met) residues. For investigation of SM-alkylated amino acids in rmCK, micro liquid chromatography-electrospray ionization high-resolution tandem-mass spectrometry measurements were performed using the Orbitrap technology. The treatment of rmCK with SM resulted in a decrease of enzyme activity. However, this decrease did only weakly correlate to the modification of Cys²⁸³ but was conclusive for the formation of Met⁷⁰-HETE and Met¹⁷⁹-HETE. In contrast, the activity of mutants of rmCK produced by side-directed mutagenesis that contained substitutions of the respective Met residues (Met⁷⁰Ala, Met¹⁷⁹Leu, and Met⁷⁰Ala/Met¹⁷⁹Leu) was highly resistant against SM. Our results point to a critical role of the surface exposed Met⁷⁰ and Met¹⁷⁹ residues for CK activity.

Vibrational spectra, NBO, HOMO-LUMO and conformational stability studies of 4-hydroxythiobenzamide

In this work, the experimental and theoretical study on molecular structure, vibrational spectral analysis of 4-hydroxythiobenzamide (HTB) have been reported. The solid phase FTIR (4000-400 cm(-1)) and FT-Raman spectra (3500-50 cm(-1)) were recorded. The molecular geometry, harmonic vibrational frequencies and bonding features of HTB in the ground-state have been calculated by the density functional method (B3LYP) with 6-311+G(d,p) and 6-311++G(d,p) as basis sets. Utilizing the observed FTIR and FT-Raman data, a complete vibrational assignment and analysis of the fundamental modes of the compound were carried out. Stability of the molecule arising from hyperconjugative interactions, charge delocalization has been analyzed using natural bond orbital (NBO) analysis. The results show that the value of electron density (ED) in the σ(∗) antibonding orbitals and E((2)) energies confirms the occurrence of ICT (intra-molecular charge transfer) within the molecule. The UV spectrum was measured in ethanol solution. The energy and oscillator strength calculated by time-dependent density functional theory (TD-DFT) correlates with the experimental findings. The calculated molecular electrostatic potential (MESP), HOMO and LUMO energies show that charge transfer occurs within the molecule. Besides, the simulated infrared and Raman spectra of the title compound which show good agreement with observed spectra.

Crystal growth, structural characterization and theoretical investigation on 3,5-dinitrosalicylic acid monohydrate for nonlinear optical applications

Organic crystal of 3,5-dinitrosalicylic acid monohydrate has been grown by slow evaporation method at room temperature, using water as solvent. Quantum chemical calculations of energies, geometric structure and vibrational analysis of the title compound are carried out by DFT method with 6-31+G (d,p) basis set. Both the experimental and theoretical spectra confirm the presence of functional groups. Electric dipole moment, polarizability and the first order hyperpolarizability values have been computed theoretically. The (1)H and (13)C nuclear magnetic resonance (NMR) chemical shifts of the molecule are calculated by the gauge independent atomic orbital (GIAO) method and compared with the experimental results. The calculated HOMO-LUMO energies confirm the charge transfer within the molecule. Thermodynamic properties (heat capacity, entropy and enthalpy) of the title compound are determined.

Study on conformational stability, molecular structure, vibrational spectra, NBO, TD-DFT, HOMO and LUMO analysis of 3,5-dinitrosalicylic acid by DFT techniques

In this work we analyzed the vibrational spectra of 3,5-dinitrosalicylic acid (3,5DNSA) molecule. The total energy of eight possible conformers can be calculated by Density Functional Theory with 6-31G(d,p) as basis set to find the most stable conformer. Computational result identify the most stable conformer of 3,5DNSA is C6. The assignments of the vibrational spectra have been carried out by computing Total Energy Distribution (TED). The molecular geometry, second order perturbation energies and Electron Density (ED) transfer from filled lone pairs of Lewis base to unfilled Lewis acid sites for 3,5-DNSA molecular analyzed on the basis of Natural Bond Orbital (NBO) analysis. The formation of inter and intramolecular hydrogen bonding between OH and COOH group gave the evidence for the formation of dimer formation for 3,5-DNSA molecule. The energy and oscillator strength calculated by Time-Dependent Density Functional Theory (TD-DFT) complements with the experimental findings. The simulated spectra satisfactorily coincides with the experimental spectra.

Conformational analysis, spectroscopic study (FT-IR, FT-Raman, UV, 1H and 13C NMR), molecular orbital energy and NLO properties of 5-iodosalicylic acid

In this study, 5-iodosalicylic acid (5-ISA, C7H5IO3) is structurally characterized by FT-IR, FT-Raman, NMR and UV spectroscopies. There are eight conformers, Cn, n=1-8 for this molecule therefore the molecular geometry for these eight conformers in the ground state are calculated by using the ab-initio density functional theory (DFT) B3LYP method approach with the aug-cc-pVDZ-PP basis set for iodine and the aug-cc-pVDZ basis set for the other elements. The computational results identified that the most stable conformer of 5-ISA is the C1 form. The vibrational spectra are calculated DFT method invoking the same basis sets and fundamental vibrations are assigned on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method with PQS program. Total density of state (TDOS) and partial density of state (PDOS) and also overlap population density of state (COOP or OPDOS) diagrams analysis for C1 conformer were calculated using the same method. The energy and oscillator strength are calculated by time-dependent density functional theory (TD-DFT) results complement with the experimental findings. Besides, charge transfer occurring in the molecule between HOMO and LUMO energies, frontier energy gap, molecular electrostatic potential (MEP) are calculated and presented. The NMR chemical shifts ((1)H and (13)C) spectra are recorded and calculated using the gauge independent atomic orbital (GIAO) method. Mulliken atomic charges of the title molecule are also calculated, interpreted and compared with salicylic acid. The optimized bond lengths, bond angles and calculated NMR and UV, vibrational wavenumbers showed the best agreement with the experimental results.

Spectroscopic (FT-IR, FT-Raman, NMR and UV-Visible) and quantum chemical studies of molecular geometry, Frontier molecular orbital, NLO, NBO and thermodynamic properties of salicylic acid

The solid phase FT-IR and FT-Raman spectra of 2-hydroxybenzoic acid (salicylic acid) have been recorded in the region 4000-400 and 4000-100 cm(-1) respectively. The optimized molecular geometry and fundamental vibrational frequencies are interpreted with the aid of structure optimizations and normal coordinate force field calculations based on density functional theory (DFT) method and a comparative study between Hartree Fork (HF) method at 6-311++G(d,p) level basis set. The calculated harmonic vibrational frequencies are scaled and they are compared with experimentally obtained FT-IR and FT-Raman spectra. A detailed interpretation of the vibrational spectra of this compound has been made on the basis of the calculated potential energy distribution (PED). The time dependent DFT method is employed to predict its absorption energy and oscillator strength. The linear polarizability (α) and the first order hyper polarizability (β) values of the investigated molecule have been computed. The electronic properties, such as HOMO and LUMO energies, molecular electrostatic potential (MEP) are also performed. Stability of the molecule arising from hyper conjugative interaction, charge delocalization has been analyzed using natural bond orbital (NBO) analysis.

Structural, vibrational and quantum chemical investigations on 5-chloro-2-hydroxybenzamide and 5-chloro-2-hydroxybenzoic acid

The Fourier transform infrared (FTIR) and FT-Raman spectra of 5-chloro-2-hydroxybenzamide (5CBA) and 5-chloro-2-hydroxybenzoic acid (5C2HBA) have been recorded in the range 4000-400 and 4000-100 cm(-1), respectively. The complete vibrational fundamental modes of the compounds were assigned and analysed using the observed FTIR and FT-Raman data. The vibrational frequencies determined experimentally were compared with the theoretical wavenumbers calculated from ab initio HF and DFT-B3LYP gradient methods employing 6-31G** and 6-311++G** basis sets. The effect of halogen, hydroxyl groups and hydrogen bonding on the characteristic frequencies of the -COOH and -CONH2 group frequencies have been investigated. In 5CBA and 5C2HBA intramolecular hydrogen bond between a hydroxyl group and CO group makes a six membered ring, which causes the O⋯H interaction onto the resonance of the benzene ring. Comparison of the positions of the ν(OH) bands shows the ν(OH) band of 5CBA is located at considerably higher frequency which confirms a weaker hydrogen bond than in 5C2HBA.

Identification of proteins containing cysteine residues that are sensitive to oxidation by hydrogen peroxide at neutral pH

A procedure for detecting proteins that contain H(2)O(2)-sensitive cysteine (or selenocysteine) residues was developed as a means with which to study protein oxidation by H(2)O(2) in cells. The procedure is based on the facts that H(2)O(2) and biotin-conjugated iodoacetamide (BIAM) selectively and competitively react with cysteine residues that exhibit a low pK(a), and that the decrease in the labeling of cell lysate proteins with BIAM caused by prior exposure of cells to H(2)O(2) or to an agent that induces H(2)O(2) production can be monitored by streptavidin blot analysis. This procedure was applied to rat pheochromocytoma PC12 cells directly treated with H(2)O(2), mouse hippocampal HT22 cells in which H(2)O(2) production was induced by glutamate, and human erythroleukemia K562 cells in which H(2)O(2) production was induced by phorbol myristate acetate. It revealed that several cell proteins contain cysteine or selenocysteine residues that are selectively oxidized by H(2)O(2). Three of these H(2)O(2)-sensitive proteins were identified as a member of the protein disulfide isomerase family, thioredoxin reductase, and creatine kinase, all of which were previously known to contain at least one reactive cysteine or selenocysteine at their catalytic sites. This procedure should thus prove useful for the identification of proteins that are oxidized by H(2)O(2) generated in response to a variety of extracellular agents.

Reactivation kinetics of 5,5'-dithiobis-(2-nitrobenzoic acid)-modified creatine kinase reactivated by dithiothreitol

The reduction of 5,5'-dithiobis-(2-nitrobenzoic acid)-modified creatine by dithiothreitol has been studied using the kinetic theory of the substrate reaction during modification of enzyme activity as previously described by C.L. Tsou (Adv. Enzymol. Rel. Areas Mol. Biol. 61 (1988) 381-436). The results show that the modified creatine kinase can be fully reactivated by an excess concentration of dithiothreitol in a monophasic kinetic course. The presence of ATP or the transition-state analogue markedly slows the apparent reactivation rate constant, while creatine shows no effect. The substrates creatine-ADP-Mg2+ can induce conformational changes of the modified enzyme but adding NO-3 cannot induce further changes that occur with the native enzyme. The reactive cysteines' location and role in the catalysis of creatine kinase are discussed. It is suggested that the cysteine may be located in the hinge area of the two domains of creatine kinase. The reactive cysteine of creatine kinase may play an important role not in the binding to the transition-state analogue but in the conformational changes caused by the transition-state analogue.

Site-specific modification of rabbit muscle creatine kinase with sulfhydryl-specific fluorescence probe by use of hydrostatic pressure

We investigated the effect of pressure on the reactivity of cysteine residues of rabbit muscle creatine kinase (CK). Performing the fluorescent modification under high pressure, a unique sulfhydryl group (Cys-253) of CK was labeled, in addition to Cys-282, which is known as a single reactive sulfhydryl under ambient conditions. CK is composed of two identical subunits, containing four cysteine residues in each subunit. Cys-282 plays an important role in enzymatic activity. In the pressure range from 0.1 MPa to 300 MPa, only one sulfhydryl group for each subunit of CK reacted with the reagents. However, at 400 MPa 2 sulfhydryl groups were modified. The 2-nitro-5-thiocyanobenzoic acid (NTCB) cleavage method revealed that both Cys-282 and Cys-253 were modified at 400 MPa. The chemical modification of Cys-282 induced a loss of enzymatic activity. By taking advantage of the modification under high pressure, selective modification of Cys-253 with 5-[N-(iodoacetamidoethyl)amino]-naphthalene-1-sulfonate (IAEDANS) was performed. A reversible blocking of Cys-282 at atmospheric pressure was followed by the reaction of Cys-253 with the fluorescent probe at 400 MPa. After the decompression, Cys-282 was unblocked, and obtained Cys-253-modified CK retained up to 64% of the catalytic activity of the intact CK. The fluorescent properties of IAEDANS covalently bound at Cys-253 were not significantly different from those of IAEDANS covalently bound at Cys-282.

High salt concentrations induce dissociation of dimeric rabbit muscle creatine kinase. Physico-chemical characterization of the monomeric species

Incubation of dimeric MM-creatine kinase (MM-CK) with high NaCl or LiCl concentrations results in dissociation of the subunits and complete enzyme inactivation. In NaCl, this process, which depends on protein concentration, may be described according to a two-state model where the dimer can be reversibly converted into compact folded monomers (D <--> 2M). At LiCl concentrations higher than 2-2.5 M, MM-CK is recovered in two monomeric states: an inactive compact species (M) and a more expanded form (EF), which represents 15-20% of the population. Thus, in LiCl, a three-state model (D <--> 2M --> 2EF) more adequately accounts for our experimental results. The monomeric species (M) obtained in NaCl and LiCl exhibits some properties of the molten globule state described in guanidine hydrochloride. Indeed, this form is compact and devoid of any enzymatic activity; it maintains a high degree of secondary structure and binds 8-anilino-1-naphthalenesulfonate. The formation of this intermediate induces the exposure of a second tryptophan (among the four present) which is located at the monomer-monomer interface in the native structure. In LiCl, the monomeric species (M) is irreversibly converted into a less compact form (EF) which seems to have lost a large part of its secondary structure.

Reversible dissociation and unfolding of dimeric creatine kinase isoenzyme MM in guanidine hydrochloride and urea

The unfolding of dimeric cytoplasmic creatine kinase (MM) by guanidine hydrochloride and by urea has been investigated using activity measurements, far-ultraviolet circular dichroism, sedimentation velocity and fluorescence energy transfer experiments to monitor global structural changes. Intrinsic (cysteine and tryptophan residues) and extrinsic probes (1-anilinonaphthalene-8-sulfonate) were also used. The reversibility of the unfolding was checked by monitoring activity and tryptophan fluorescence. The unfolding of creatine kinase in guanidine hydrochloride is a reversible multistep process, as suggested by the non-coincidence of denaturation curves at equilibrium. Inactivation of the dimer precedes its dissociation into two monomers and an intermediate state was identified during the unfolding of the monomer. This intermediate state is characterized by a relatively high degree of secondary structure (as shown by far-ultraviolet circular dichroism), of compactness (as shown by fluorescence energy transfer measurements and sedimentation experiments), a fluctuating tertiary structure (as shown by near-ultraviolet circular dichroism) and a strong affinity for anilinonaphthalene sulfonate (as demonstrated by fluorescence). These results clearly indicate that the intermediate state detected possesses some of the properties of a molten globule. In urea, the unfolding pathway is reversible but differs from that observed in guanidine hydrochloride. Indeed inactivation, dissociation and loss of tertiary structure are coincident but the ellipticity curve is slightly shifted to a higher urea concentration. The dimer is dissociated into two expanded monomers possessing some secondary structure which is progressively lost at a higher urea concentration (6.4M). These results show that guanidine hydrochloride is approximately six times more effective than urea for inactivation and dissociation, underlining the fact that electrostatic interactions are very important in the stabilization of the active site and of the dimeric state.

Creatine kinase compactness and thiol accessibility during sodium dodecyl sulfate denaturation estimated by resonance energy transfer and 2-nitro-5-thiocyanobenzoic acid cleavage

We have investigated the effect of increasing sodium dodecyl sulfate (SDS) concentrations on rabbit muscle cytosolic creatine kinase structure by two methods. We have first determined the variation of accessibility of the thiol groups of the enzyme during SDS denaturation by a technique which involves an irreversible chemical modification of CK accessible thiol groups, followed by NTCB cleavage before the unmodified cysteines in 8 M urea (pH 9) and analysis of the peptides obtained by resolutive gel electrophoresis, without sequencing. We have determined that the order of accessibility of CK MM cysteine residues during SDS denaturation is Cys-282, Cys-145 and then Cys-253. The fourth cysteine residue, Cys-73, is never titrated even at high SDS/CK molar ratio. In contrast, the three last residues are simultaneously titrated when CK is denatured in guanidinium chloride. Thus, SDS-denatured CK seems to retain some residual organized structure. In order to confirm this hypothesis, compactness of the molecule was estimated by fluorescence energy transfer between CK tryptophans and AEDANS, an extrinsic fluorophore. The location of this fluorophore on the accessible thiol of Cys-282 was verified by the previous technique. The results of these experiments do indicate that SDS-denatured CK is more compact than CK completely unfolded in guanidinium chloride.

An equilibrium study of the dependence of secondary and tertiary structure of creatine kinase on subunit association

Several physical properties of dimeric creatine kinase in increasing concentrations of guanidine hydrochloride (GDN/HCl) were evaluated and correlated with degree of subunit dissociation, determined by isozyme competitive hybridization. Three distinct stages were observed that correlated with phases before, during and after dissociation. In 0.2 M GDN/HCl, before significant dimer dissociation, creatinine kinase has 75% of its original activity, and exhibits only small decreases in circular dichroism, intrinsic fluorescence and emission maximum. The spectral characteristics of creatine kinase (CK) derivatized with 5-[(((2-iodoacetyl)amino)ethyl)amino]naphthalene-1- sulfonate (AEDANS-CK) at the cysteine near the active site are suggestive of a slightly more non-polar environment. A decrease in steady-state anisotropy (0.140 to 0.132) was characterized by time-resolved methods. The slow component of the time-resolved anisotropy decay law, which reflects global protein rotation, is decreased only from 36.6 to 33.4 ns. The faster component decreases from 1.95 to 0.74 ns which suggests the active-site domain is more sensitive to conformation perturbation than the protein as a whole. Overall these observations suggest the subunits within the dimeric state are rather stable in dilute denaturant, but undergo a minor contraction in conformation. The region of the active site, as reported by the extrinsic fluorophore, is less polar but apparently more flexible in dilute denaturant. Between 0.5 M and 1 M GDN/HCl, most of the dimers dissociate, 63% of helical content is lost and inactivation is complete. The intrinsic fluorescence shifts 8 nm to the red and increases by 35%, indicating exposure of tryptophans to solvent and release of quenching, perhaps between residues on separate subunits. Over the same denaturant range, the spectral characteristics and lifetime of AEDANS-CK suggests less exposure of the active site to solvent. Time-resolved anisotropy measurements show that the sharp decrease in steady-state anisotropy to 0.086 is due to a decrease in macromolecular rotation to 22 ns. This may represent the rotational correlation time of a relatively intact subunit, and suggests limited subunit unfolding accompanying dissociation. Dissociation is complete in 1.5 M GDN/HCl. The subunits still retain 20% helical content in 2 M denaturant and not until 5 M GDN/HCl is all helical structure eliminated. Above 2 M GDN/HCl, AEDANS-CK exhibits sharp decreases in steady-state anisotropy, fluorescence lifetime and the long-lived component in the time-resolved anisotropy decay law. These results reveal a catastrophic loss of tertiary structure by the subunits and may define the physical properties of the random coil.

The activity of S-thiomethyl modified creatine kinase is due to the regeneration of free thiol at the active site

Creatine kinase modified by S-methyl methanethiosulfonate and devoid of reactive thiol group has been reported to retain about 18-40% of the activity of the native enzyme. It has now been found that during the reaction catalyzed by the modified enzyme the rate increases with time and if the reaction is allowed to continue sufficiently long, the enzyme eventually recovers full activity. The presence of substrates is not required for the reactivation as suitable dilution after removal of MMTS in excess leads to complete reactivation of the MMTS modified enzyme with the simultaneous regeneration of reactive thiol per each dimeric molecule as shown by determinations with DTNB and IAN. The addition of MMTS during the course of reactivation again inactivates the reactivated enzyme. The activity recovery is therefore due to the regeneration of reactive thiol and it appears that the active-site thiols are essential for the activity of rabbit muscle creatine kinase.

Heterogeneous flexibilities of the active site domains of homodimeric creatine kinase: effect of substrate

(1) A single subunit and both subunits of creatine kinase from rabbit muscle was derivatized at the active site with the thiol-specific reagent 2-(4'-(iodoacetamido)anilino)-naphthalene-6-sulfonic acid. (2) The highly biphasic kinetics of the labelling reaction were characterized from measurements of activity, steady-state fluorescence and anisotropy. Derivatization of one thiol and both thiols resulted in 48 and 100% inhibition, respectively. The dead-end complex (DEC), consisting of creatine, MgADP and protein, inhibited the rate, but not the extent, of derivatization and resulted in a 2-fold increase in fluorescence. (3) The fluorescence of singlylabelled (1AANS/CK) and doublylabelled (2AANS/CK) protein exhibited three discrete lifetime components or a two-term Lorentzian distribution. The decay laws for both preparations were not remarkably different, except that, unlike 1AANS/CK, the longer decay component of 2AANS/CK was distributed, which narrowed in the presence of the DEC. (4) The steady-state anisotropies of 1AANS/CK and 2AANS/CK at 25 degrees C were 0.305 and 0.240, respectively. It was concluded that the fast reacting site was immobile and the slow reacting site was flexible. Kinetics of labelling and anisotropy emission spectra indicated that the DEC immobilized the flexible site. (5) The anisotropy decay of 1AANS/CK with and without the DEC was described by a rotational correlation time of about 50 ns, characteristic of the molecular rotation of the CK dimer. At least two terms were required to fit the data for 2AANS/CK, indicating additional segmental motion which was eliminated upon formation of the DEC. (6) Energy transfer from tryptophans to AANS indicated movement of approx. 3 A accompanying formation of the DEC.

A physicochemical comparison of the isozymes of creatine kinase from rabbit brain and muscle

A comparison of specific structural features of creatine kinase from rabbit muscle and brain was undertaken to determine if the observed isozyme specific differences in catalytic cooperativity are related to conformational differences, particularly differences in packing density. The intrinsic fluorescence of the brain isozyme is 2-fold higher than the muscle isozyme. In the denatured state, both proteins display the characteristic red shift in emission maximum; however, the emission intensity of the brain isozyme increases only 5% upon denaturation compared to nearly 100% increase for the muscle protein. The fluorescence lifetimes are 2.65 ns (67%) and 0.48 ns for native muscle enzyme and 4.38 ns (65%) and 0.80 ns for brain enzyme. Upon denaturation, the lifetimes are 3.98 ns (77%) and 0.99 ns for muscle protein and 3.82 ns (79%) and 0.86 ns for brain protein. Stern-Volmer plots of quenching by acrylamide are essentially the same for both native isozymes indicating that the differences of the intrinsic fluorescence of the native proteins are not due to differences in solvent accessibility. The spectral and lifetime differences in the isozymes in the native state and changes accompanying denaturation are consistent with the occurrence of energy transfer in native muscle isozyme. The rotational correlation times of 5-[2-(iodoacetyl)aminoethyl]aminonaphthalene-1-sulfonate conjugated proteins, derivatized at the active site reactive thiol, are best described by two term decay laws. The slower rotations, 45.1 ns (75%) and 40.6 ns (71%) reflect overall macromolecular rotation for the muscle and brain isozymes, respectively. The faster motions, 2.4 ns for muscle isozyme and 0.4 ns for the brain isozyme, are attributed to the probe or probe associated segmental motions and indicate these motions are more restricted in the muscle protein. Reactivity of creatine kinase (2.5-10 microM) with the amino-specific reagent trinitrobenzene sulfonate (0.4-2 mM) was analyzed by pseudo-first-order and second order models, neither of which was adequate for the entire range of data. However, in every case, the rate constants were faster for brain creatine kinase but the extent of reaction was greater for muscle creatine kinase. The faster initial reactivity of the brain isozyme is consistent with greater accessibility for lysine derivatization.(ABSTRACT TRUNCATED AT 400 WORDS)

Resonance energy transfer between the active sites of creatine kinase from rabbit brain

Resonance energy transfer was measured between the active site domains of the brain isozyme of creatine kinase (CK-BB). The reactive thiol near the active sites, one on each subunit of the dimeric protein, was derivatized using 5-[2-[iodoacetyl)amino)ethyl]aminonaphthalene-1-sulfonic acid (AED), 2-[4'-iodoacetamidoanilino]naphthalene-6-sulfonic acid (AANS) and 5-iodoacetamidofluorescein (AF). Suitable donor/acceptor protein conjugated hybrids were prepared by controlled kinetics producing CK-BB-AED/AF and CK-BB-AANS/AF. Transfer efficiencies, measured from the quenching of the donor lifetime and steady-state sensitized acceptor emission, ranged from 0.10 to 0.17. From determination of the donor/acceptor overlap integrals, donor quantum yields and attempts to delimit the orientation factor using steady-state and phase-resolved anisotropy measurements, it was found that a suitable estimate of the range between the active sites was between 45 and 57 A. This range is similar to that reported previously for the muscle isozyme of creatine kinase (Grossman, S.H. (1989) Biochemistry 28, 4894-4902) but is a significantly greater distance than detected for the hybrid, myocardial specific isozyme (Grossman, S.H. (1983) Biochemistry 22, 5369-5375).

Is the subunit the minimal function unit of creatine kinase?

The dimeric rabbit muscle isozyme of creatine kinase (MM) is modified by iodoacetamide to produce the inactive dimer (M'M') and then hybridized with native dimeric brain isozyme (BB). The hybrid enzyme (M'B), as isolated by PAGE, has the same Km for both ATP and creatine but half the specific activity of the brain isozyme (BB). Likewise, the hybrid of the modified brain with the native muscle isozyme (MB') has half the activity of the native muscle enzyme. The M'B, MB' and MB hybrid dimers all have essentially the same electrophoretic properties, and their intrinsic fluorescence and CD spectra in the far-ultraviolet region are very similar to those of the homodimers MM and BB. Similar results were obtained for the hybrid (M"B) containing the muscle enzyme subunit modified at both the thiol group with iodoacetamide and the Trp residue with dimethyl(2-hydroxy-5-nitrobenzyl)sulfonium bromide and the native brain enzyme submit. The above results suggest strongly the independent catalytic function of the subunit of creatine kinase.

Creatine kinase is modified by 2-chloromercuri-4-nitrophenol at the active site thiols with complete inactivation

Creatine kinase modified by mercurials has been reported to be fully reactive as the native enzyme. This was ascribed to the modification of a second class of thiol groups instead of the reactive thiols at the active site (Laue, M.C. and Quiocho, F.A. (1977) Biochemistry 16, 3838-3845). It has now been shown by spectrophotometric titration and fluorescence studies that 2-chloromercuri-4-nitrophenol (MNP) reacts preferentially with the active-site thiol. Moreover, if the activity of the modified enzyme is determined in the absence of added bovine serum albumin or other enzymes, as usually employed in coupled activity assay systems for creatine kinase, the modified enzyme is completely inactive. Addition of an excess of bovine serum albumin or rabbit muscle glyceraldehyde-3-phosphate dehydrogenase restores the activity of the enzyme to over 80% of its original level. It appears that the active thiol groups at the active site of creatine kinase are after all modified by MNP with complete inactivation.

Resonance energy transfer between the active sites of rabbit muscle creatine kinase: analysis by steady-state and time-resolved fluorescence

Resonance energy transfer between the reactive thiols of rabbit muscle creatine kinase was evaluated. The reactive thiols are located at the active site, one occurring on each subunit of the dimeric protein that is known to be a constituent of the M-line structure of the myofibril. Transfer efficiency was evaluated from energy donor quenching of fluorescence by steady-state and phase-modulation lifetime measurements and determination of sensitized emission of the acceptor. Several sulfhydryl-specific donor fluorophores were used including 5-[[[(iodoacetyl)amino]ethyl]amino]naphthalene-1-sulfonic acid, 7-(dimethylamino)-3-(4-maleimidylphenyl)-4-methylcoumarin, and 2-[4-(iodoacetamido)anilino]naphthalene-6-sulfonic acid (IAANS). Energy transfer acceptors included 5-(iodoacetamido)fluorescein and the nonfluorescent dye [4-[[4-(dimethylamino)phenyl]azo]phenyl]iodoacetamide. In order to prepare the necessary homodimer labeled with both donor and acceptor, advantage was taken of the biphasic reaction between creatine kinase and IAANS. In some instances, donor/acceptor hybrids were prepared by denaturation/renaturation procedures, and possible deviations from expected hybridization stoichiometry were considered. Disproportionation of singly labeled dimers (to unlabeled and doubly labeled dimers) was not observed when the brain isozyme of creatine kinase was used to trap dissociated dye-conjugated or unlabeled muscle-type subunits of creatine kinase. From studies of five different donor/acceptor combinations, the efficiency of energy transfer was found to occur over a range of 5-14%, indicating that the reactive thiols are well separated. Overlap integrals and quantum yields were evaluated, and estimates of the range of orientation factor were obtained to determine a range for the distance between the active sites of creatine kinase. When the ranges are overlapped, a limited distance of 48.6-60.4 A is obtained.(ABSTRACT TRUNCATED AT 250 WORDS)

Fluorescent labeling of cysteinyl residues to facilitate electrophoretic isolation of proteins suitable for amino-terminal sequence analysis

A protein labeling procedure which enables detection of subpicomole quantities of proteins on sodium dodecyl sulfate (SDS)-polyacrylamide gels is described. Proteins are rendered fluorescent by reduction of disulfide bonds with dithiothreitol followed by alkylation with 5-N-[(iodoacetamidoethyl)amino]naphthalene-1-sulfonic acid (5-I-AEDANS) or 5-iodoacetamido-fluorescein. Labeling is performed prior to electrophoresis, thus eliminating the need for staining with dyes and destaining after electrophoresis. As little as 375 fmol (25 ng) of prelabeled bovine serum albumin can be readily visualized after electrophoresis. Bands are still visible after electrophoretic transfer to nitrocellulose. Simultaneous labeling of proteins in complex mixtures is possible using this technique. This includes cysteine containing proteins of disrupted Newcastle disease virus. The magnitudes of the molecular weight increases which occur upon labeling reflect the cysteine contents of proteins. The mode of chemical modification for the prelabeling procedure was chosen because of its compatibility with analytical techniques, such as amino acid analysis, peptide mapping, or sequence analysis, which may be applied to the protein after electroelution from SDS-acrylamide gels. It replaces the need for reduction and carboxymethylation prior to these analytical procedures. Protein-sequence analysis of prelabeled bovine serum albumin, including samples electroeluted from SDS-acrylamide gels, has justified the choice of this method to facilitate isolation of proteins for sequence analysis. Equivalent sequence data were obtained with reduced bovine serum albumin S-alkylated with iodoacetic acid or 5-I-AEDANS.

Anion activation of monkey muscle creatine kinase

Creatine kinase from rhesus monkey skeletal muscle is activated by acetate and other short chain fatty acids. Activation is associated with lower Km and higher Vmax values at less than saturating substrate concentrations but does not occur when both substrates are saturating. No co-operativity between subunits is evident in the activation process. It appears that acetate promotes the mutual enhancement by substrates in their binding by inducing the optimum enzyme conformation normally associated with substrate saturation. Conservation of this activation effect through the evolution of the phosphagen kinases implies that it may well be of physiological significance.

The refolding of denatured rabbit muscle creatine kinase. Search for intermediates in the refolding process and effect of modification at the reactive thiol group on refolding

A number of aspects of the refolding of denatured rabbit muscle creatine kinase have been studied. Addition of substrates has no effect on the rate or extent of regain of activity. The changes in protein fluorescence during refolding broadly parallel the regain of activity. A study of the susceptibility of the enzyme to proteolysis during refolding indicates that there is no significant accumulation of folded, but inactive, intermediates in the folding process. Modification of the reactive thiol group on each subunit of the enzyme by small reagents such as iodoacetate or iodoacetamide prior to denaturation has only a small effect on the rate of subsequent refolding. However, modification by the bulky reagent 6-(4-iodoacetamidophenyl)aminonaphthalene-2-sulphonate has a very large effect on the ability of the enzyme to refold after denaturation.

The effect of limited proteolysis on rabbit muscle creatine kinase

Creatine kinase from rabbit muscle is inactivated by limited proteolysis with proteinase K from Tritirachium album. Gel-filtration and cross-linking studies showed that the limited proteolysis did not affect the molecular weight of the enzyme under non-denaturing conditions, but did cause changes in the reactivity of the reactive thiol group on each subunit and in the ability of the enzyme to form a 'transition-state analogue' complex in the presence of magnesium acetate plus ADP plus creatinine plus NaNO3.

The reaction of rabbit muscle creatine kinase with diethyl pyrocarbonate

The reaction of rabbit muscle creatine kinase with diethyl pyrocarbonate was studied. It was found that up to five of the sixteen histidine groups per enzyme subunit could be modified, and under the conditions employed, there was no evidence for formation of the disubstituted derivative of histidine. Evidence was obtained for small but significant amounts of modification of lysine and cysteine groups; tyrosine groups were not modified. Modification of the enzyme led to inactivation; this could be protected against by inclusion of substrates or, more effectively, by inclusion of the combination MgADP plus creatine plus nitrate, which is thought to produce a 'transition-stage-analogue' complex. Analysis of data on the rates of inactivation and the stoicheiometry of modification suggested that there was one essential histidine group per enzyme subunit, modification of which led to inactivation.