A study of the role of the reactive thiol group of rabbit muscle creatine kinase with a chromophoric reporter group

ADP-binding and ATP-binding sites in native and proteinase-K-digested creatine kinase, probed by reaction-induced difference infrared spectroscopy

Conformational changes induced by nucleotide binding to native creatine kinase (CK) from rabbit muscle and to proteinase-K-digested (nicked) CK, were investigated by infrared spectroscopy. Photochemical release of ATP from ATP[Et(PhNO2)] in the presence of creatine and native CK produced reaction-induced difference infrared spectra (RIDS) of CK related to structural changes of the enzyme that paralleled the reversible phosphoryl transfer from ATP to creatine. Similarly the photochemical release of ADP from ADP[Et(PhNO2)] in the presence of phosphocreatine and native CK allowed us to follow the backward reaction and its corresponding RIDS. Infrared spectra of native CK indicated that carboxylate groups of Asp or Glu, and some carbonyl groups of the peptide backbone are involved in the enzymatic reaction. Native and proteinase nicked CK have similar Stokes' radii, tryptophan fluorescence, fluorescence fraction accessible to iodide, and far-ultraviolet CD spectra, indicating that native and modified enzymes have the same quaternary structures. However, infrared data showed that the binding site of the gamma-phosphate group of the nucleotide was affected in nicked CK compared with that of the native CK. Furthermore, the infrared absorptions associated with ionized carboxylate groups of Asp or Glu amino acid residues were different in nicked CK and in native CK.

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.

Changes of creatine kinase secondary structure induced by the release of nucleotides from caged compounds. An infrared difference-spectroscopy study

Light-induced release of ADP and ATP from their respective caged nucleotides produced small distinct difference infrared spectra of creatine kinase (CK), indicating that ADP and ATP binding to CK promoted different structural alteration. The positive band at 1638-1640 cm-1 and the negative band at about 1650-1652 cm-1 on the reaction-induced infrared difference spectra in the amide I region were insensitive to the deuteration effects. They were assigned to the peptide backbone of the ADP/ATP-binding site. In addition Pi or ATP binding produced another positive band at 1657-1659 cm-1 corresponding to the C = O (amide I band) associated with the gamma-phosphate of ATP. This site was also affected when ADP was added, indicating coupling interactions between both sites. No additional structural changes were observed when creatine and ADP were added, suggesting that the creatine-binding site was uncoupled from the ADP-binding site. The infrared difference spectra of a transition-state-analog complex formed by the addition of ADP, creatine and NO3- (a planar-phosphate-mimicking group) lacked the 1657-1659-cm-1 band indicating that the binding site of gamma-phosphate within CK, was not affected. Infrared changes in the 1560-1590-cm-1 region suggested that carboxylate groups of Asp or Glu were involved in the binding of Pi, ADP and ATP.

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.

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.

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.

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.

Inhibition of creatine kinase by iodoalkanes. Further appraisal of the essential nature of the reactive thiol group

Creating kinase (ATP: creatine N-phosphotransferase) is completely inhibited by low molecular weight iodoalkanes in a pseudo first order reaction. Analysis of this and other data suggests that covalent modification per se is not a sufficient criterion to establish whether or not an enzyme group is essential for catalysis.

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

The dimeric enzyme creatine kinase from rabbit muscle was treated with three derivatives of iodoacetamide that are capable of introducing fluorescent groups into the enzyme. All the three reagents (4-iodoacetamidosalicylate (IAS), 5-[N-(iodoacetamidoethyl)amino]-naphthalene-1-sulphonate (IAEDANS) and 6-(4-iodoacetamidophenyl)aminonaphthalene-2-sulphonate (IAANS)) were shown to react at the same single thiol group on each enzyme subunit, leading to complete inactivation of the enzyme. The reaction with IAS was extremely rapid by comparison with the reaction with iodoacetamide or iodoacetate, but various lines of evidence suggest that IAS is not a true affinity label. However, kinetic and binding studies indicate that salicylate itself probably binds at the nucleotide-binding site on the enzyme. As the size of the modifying reagent increased, the first thiol group reacted more rapidly than the second; this trend was more pronounced at 0 degree C than at 25 degree C. With the largest modifying reagent used (IAANS), the pronounced biphasic nature of the modification reaction permitted the preparation of a hybrid enzyme in which only one subunit was modified, but a study of the thiol-group reactivity showed that this hybrid enzyme preparation underwent subunit rearrangement.