12 Creatine Kinase (Adenosine 5′-Triphosphate-Creatine Phosphotransferase)

Diversity of phosphagen kinases in annelids: The first sequence report for a putative opheline kinase

Opheline kinase (OK) is one of the phosphagen kinases (PKs) restricted to annelids, but the amino acid sequence has not been determined yet. The OK enzyme was isolated in 1966 from the polychaete Ophelia neglecta (Opheliidae) and shown to have somewhat broader activities for the various substrates opheline, lombricine and taurocyamine. To determine the OK sequence, we analyzed the RNA sequencing data for Ophelina sp. and Thoracophelia sp., belonging to Opheliidae. Four PK sequences, namely, taurocyamine kinase (TK), creatine kinase (CK), mitochondrial CK (MiCK) and putative OK, were identified in both species, and the recombinant Ophelina enzymes were expressed in E. coli and purified. Since the substrate opheline was not commercially available, we used the partial activity toward taurocyamine to infer the enzyme specificity. The putative Ophelina OK showed lower activity to taurocyamine with a V_max/K_m nearly identical to a previously published value for an OK from a related species Ophelia neglecta. Under the same conditions, the true Ophelina TK showed much higher activity. Thus, the putative Ophelina enzyme was determined to be OK. The amino acid sequence alignment indicated that Ophelina and Thoracophelia OKs have five amino acid deletions in the GS region, like those of LKs and AKs, and the guanidino substrate specific residue was Lys, the same as LKs. In the phylogenetic tree constructed from annelid PK amino acid sequences, the OK sequences formed a distinct cluster, and it was placed near the TK and lombricine kinase (LK) clusters. This is the first report of the amino acid sequence for the OK enzyme.

Characterization of the arginine kinase isoforms in Caenorhabditis elegans

Phosphagen kinases (PKs) are well-studied enzymes involved in energy homeostasis in a wide range of animal, protozoan, and even some bacterial species. Recent genome efforts have allowed comparative work on the PKs to extend beyond the biochemistry of individual proteins to the comparative cellular physiology and examining of the role of all PK family members in an organism. The sequencing of the Caenorhabditis elegans genome and availability of sophisticated genetic tools within that system affords the opportunity to conduct a detailed physiological analysis of the PKs from a well known invertebrate for comparison with the extensive work conducted on vertebrate systems. As a first step in this effort we have carried out a detailed molecular genetic and biochemical characterization of the PKs in C. elegans. Our results reveal that C. elegans has five PK genes encoding arginine kinases that range in catalytic efficiency (kcat/KM(Arg)) from (3.1±0.6)×10(4) to (9±4)×10(5) M(-1) s(-1). This range is generally within the range seen for arginine kinases from a variety of species. Our molecular genetic and phylogenetic analysis reveals that the gene family has undergone extensive intron loss and gain within the suborder Rhabditina. In addition, within C. elegans we find evidence of gene duplication and loss. The analysis described here for the C. elegans AKs represents one of the most complete biochemical and molecular genetic analysis of a PK family within a genetically tractable invertebrate system and opens up the possibility of conducting detailed physiological comparisons with vertebrate systems using the sophisticated tools available with this model invertebrate system.

Evolution of the diverse array of phosphagen systems present in annelids

Annelids as a group express a variety of phosphagen kinases including creatine kinase (CK), glyocyamine kinase (GK), lombricine kinase (LK), taurocyamine kinase (TK) and a unique arginine kinase (AK) restricted to annelids. In prior work, we have determined and compared the intron/exon organization of the annelid genes for cytoplasmic GK, LK, AK, and mitochondrial TK and LK (MiTK and MiLK, respectively), and found that these annelid genes, irrespective of cytoplasmic or mitochondrial, have the same 8-intron/9-exon organization strikingly similar to mitochondrial CK (MiCK) genes. These results support the view that the MiCK gene is basal and ancestral to the phosphagen kinases unique to annelids. To gain a greater understanding of the evolutionary processes leading to the diversity of annelid phosphagen kinases, we determined for the first time the intron/exon organization of a cytoplasmic CK gene from a polychaete as well as that of another polychaete MiCK gene. These gene structures, coupled with a phylogenetic analyses of annelid enzymes and assessment of the fidelity of substrate specificity of some these phosphagen kinases, provide insight into the pattern of radiation of the annelid enzymes. Annelid phosphagen kinases appeared to have diverged in the following order (earliest first): (1) cytoplasmic AK, LK and TK, (2) GK, and (3) mitochondrial MiLK and MiTK. Interestingly, phylogenetic analyses showed that the above phosphagen kinases appear to be basal to all CK isoforms (mitochondrial, cytoplasmic and flagellar CKs). This somewhat paradoxical placement of CKs most likely reflects a higher rate of evolution and radiation of the annelid-specific LK, TK and GK genes than the CK isoform genes.

Changing the substrate specificity of creatine kinase from creatine to glycocyamine: evidence for a highly evolved active site

Eight variants of creatine kinase were created to switch the substrate specificity from creatine to glycocyamine using a rational design approach. Changes to creatine kinase involved altering several residues on the flexible loops that fold over the bound substrates including a chimeric replacement of the guanidino specificity loop from glycocyamine kinase into creatine kinase. A maximal 2,000-fold change in substrate specificity was obtained as measured by a ratio of enzymatic efficiency (k(cat)/K(M).K(d)) for creatine vs. glycocyamine. In all cases, a change in specificity was accompanied by a large drop in enzymatic efficiency. This data, combined with evidence from other studies, indicate that substrate specificity in the phosphagen kinase family is obtained by precise alignment of substrates in the active site to maximize k(cat)/K(M).K(d) as opposed to selective molecular recognition of one guanidino substrate over another. A model for the evolution of the dimeric forms of phosphagen kinases is proposed in which these enzymes radiated from a common ancestor that may have possessed a level of catalytic promiscuity. As mutational events occurred leading to greater degrees of substrate specificity, the dimeric phosphagen kinases became evolutionary separated such that the substrate specificity could not be interchanged by a small number of mutations.

Transition state stabilization by six arginines clustered in the active site of creatine kinase

Six fully conserved arginine residues (R129, R131, R235, R291, R319, and R340) closely grouped in the nucleotide binding site of rabbit muscle creatine kinase (rmCK) were mutated; four to alanine and all six to lysine. Kinetic analyses in the direction of phosphocreatine formation showed that all four alanine mutants led to substantial losses of activity with three (R129A, R131A, and R235A) having no detectable activity. All six lysine mutants retained variable degrees of reduced enzymatic activity. Static quenching of intrinsic tryptophan fluorescence was used to measure the binding constants for MgADP and MgATP. Nucleotide binding was at most only modestly affected by mutation of the arginine residues. Thus, the cluster of arginines seem to be primarily responsible for transition state stabilization which is further supported by the observation that none of the inactive mutants demonstrated the ability to form a transition analogue complex of MgADP.nitrate.creatine as determined by fluorescence quenching assays. As a whole, the results suggest that the most important role these residues play is to properly align the substrates for stabilization of the phosphoryl transfer reaction.

Free Radicals Mediate Cardiac Toxicity Induced by Adriamycin

Anthracycline antibiotics, including adriamycin (ADM), are widely used to treat various human cancers, but their clinical use has been limited because of their cardiotoxicity. ADM is especially toxic to heart tissue. The mechanisms responsible for the cardiotoxic effect of ADM have been very/extremely controversial. This review focuses on the participation of free radicals generated by ADM in the cardiotoxic effect. ADM is reduced to a semiquinone radical species by microsomal NADPH-P450 reductase and mitochondrial NADH dehydrogenase. In the presence of oxygen, the reductive semiquinone radical species produces superoxide and hydroxyl radicals. Generally, lipid peroxidation proceeds by mediating the redox of iron. ADM extracts iron from ferritin to form ADM-Fe3+, which causes lipid peroxidation of membranes. These events may lead to disturbance of the membrane structure and dysfunction of mitochondria. However, superoxide dismutase and hydroxyl radical scavengers have little effect on lipid peroxidation induced by ADM-Fe3+. Alternatively, ADM is oxidatively activated by peroxidases to convert to an oxidative semiquinone radical, which participates in inactivation of mitochondrial enzymes or including succinate dehydrogenase and creatine kinase. Here, we discuss the activation of ADM and the role of reductive and oxidative ADM semiquinone radicals in the cardiotoxic effect of this antibiotic.

Inactivation of creatine kinase induced by quercetin with horseradish peroxidase and hydrogen peroxide. pro-oxidative and anti-oxidative actions of quercetin

Pro-oxidative and anti-oxidative actions of quercetin were examined through inactivation of CK and inhibition of lipid peroxidation. Quercetin induced inactivation of creatine kinase (CK) during the interaction with horseradish peroxidase and hydrogen peroxide (HRP-H(2)O(2)). CK activity in heart homogenate was also reduced by quercetin with HRP-H(2)O(2). Flavonoids that have a catechol structure in the B ring, such as taxifolin, catechin and luteolin, also induced CK inactivation. These flavonoids strongly inhibited NADPH and ADP-Fe(3+)-dependent microsomal lipid peroxidation. These results suggest a close relationship between pro-oxidative and anti-oxidative actions of quercetin. Electron spin resonance (ESR) signals of the quercetin radical was emitted during the interaction of quercetin with HRP-H(2)O(2) in the presence of Zn(2+) as a stabilizer. Adding CK diminished the ESR signals of quercetin radicals, suggesting CK efficiently scavenged quercetin radicals. Sulfhydryl groups and tryptophan residues in CK decreased during the interaction of quercetin with HRP-H(2)O(2). The kinetic parameters of K(m) and V(max) for ADP and creatine phosphate changed rapidly, suggesting that the inactivation of CK was induced through conformational change of the enzyme. Glyceraldehyde-3-phosphate dehydrogenase had a higher sensitivity to quercetin with HRP-H(2)O(2) than CK. Quercetin radicals may mediate between pro-oxidative and anti-oxidative action.

Inactivation of creatine kinase during the interaction of mefenamic acid with horseradish peroxidase and hydrogen peroxide: participation by the mefenamic acid radical

Creatine kinase (CK) was used as a marker molecule to examine the side effects of damage to tissues by mefenamic acid, an effective drug to treat rheumatic and arthritic diseases, with horseradish peroxidase and hydrogen peroxide (HRP-H(2)O(2)). Mefenamic acid inactivated CK during its interaction with HRP-H(2)O(2). Also, diphenylamine and flufenamic acid caused a loss of CK activity, indicating the imino group, not substituent groups, in the phenyl rings have a crucial role in CK inactivation. Rapid change in mefenamic acid spectra was detected, suggesting that mefenamic acid is efficiently oxidized by HRP-H(2)O(2). Peroxidases oxidize xenobiotics to free radicals by a one-electron transfer. However, direct detection of mefenamic acid radicals by electron spin resonance (ESR) was unsuccessful. Reduced glutathione and 5,5-dimethyl-1-pyrroline-1-oxide (DMPO) in the reaction mixture containing mefenamic acid with HRP-H(2)O(2) produced ESR signals consistent with a DMPO-glutathionyl radical adduct. These results suggest that inactivation of CK is probably caused through formation of mefenamic acid radicals. Sulfhydryl groups and tryptophan residues of CK were diminished by mefenamic acid with HRP-H(2)O(2). Other SH enzymes, including alcohol dehydrogenase and glyceraldehyde-3-phosphate dehydrogenase, were very sensitive to mefenamic acid with HRP-H(2)O(2). Inactivation of SH enzymes may explain some deleterious actions of mefenamic acid.

Inactivation of mitochondrial succinate dehydrogenase by adriamycin activated by horseradish peroxidase and hydrogen peroxide

Although human cancers are widely treated with anthracycline drugs, these drugs have limited use because they are cardiotoxic. To clarify the cardiotoxic action of the anthracycline drug adriamycin (ADM), the inhibitory effect on succinate dehydrogenase (SDH) by ADM and other anthracyclines was examined by using pig heart submitochondrial particles. ADM rapidly inactivated mitochondrial SDH during its interaction with horseradish peroxidase (HRP) in the presence of H(2)O(2) (HRP-H(2)O(2)). Butylated hydroxytoluene, iron-chelators, superoxide dismutase, mannitol and dimethylsulfoxide did not block the inactivation of SDH, indicating that lipid-derived radicals, iron-oxygen complexes, superoxide and hydroxyl radicals do not participate in SDH inactivation. Reduced glutathione was extremely efficient in blocking the enzyme inactivation, suggesting that the SH group in enzyme is very sensible to ADM activated by HRP-H(2)O(2). Under anaerobic conditions, ADM with HRP-H(2)O(2) caused inactivation of SDH, indicating that oxidized ADM directly attack the enzyme, which loses its activity. Other mitochondrial enzymes, including NADH dehydrogenase, NADH oxidase and cytochrome c oxidase, were little sensitive to ADM with HRP-H(2)O(2). SDH was also sensitive to other anthracycline drugs except for aclarubicin. Mitochondrial creatine kinase (CK), which is attached to the outer face of the inner membrane of muscle mitochondria, was more sensitive to anthracyclines than SDH. SDH and CK were inactivated with loss of red color of anthracycline, indicating that oxidative activation of the B ring of anthracycline has a crucial role in inactivation of enzymes. Presumably, oxidative semiquinone or quinone produced from anthracyclines participates in the enzyme inactivation.

Inactivation of creatine kinase during the interaction of indomethacin with horseradish peroxidase and hydrogen peroxide: involvement of indomethacin radicals

Creatine kinase (CK) was used as a marker molecule to examine the side effect of damage to tissues by indomethacin (IM), an effective drug to treat rheumatoid arthritis and gout, with horseradish peroxidase and hydrogen peroxide (HRP-H2O2). IM inactivated CK during its interaction with HRP-H2O2. Under aerobic conditions, inactivation of CK significantly decreased. CK in rat heart homogenate was also inactivated by IM with HRP-H2O2. When IM was incubated with HRP-H2O2, the maximum absorption of IM at 280 nm rapidly decreased and a new peak at 410 nm occurred with isosbestic points at 260 and 312 nm. In contrast, under anaerobic conditions, the spectral change of IM was almost absent, indicating IM was oxidized to the yellow substance by HRP-H2O2. Adding catalase strongly inhibited the production of yellow substance. Sodium azide also blocked the formation of yellow substance and the inactivation of CK. Electron spin resonance signals of IM carbon-centered radical were detected using 2-methyl-2-nitrosopropane during the interaction of IM with HRP-H2O2 under anaerobic conditions. Oxygen was consumed during the interaction of IM with HRP-H2O2. These results suggest that IM carbon-centered radicals may rapidly react with O2 to generate the peroxyl radicals. Sulfhydryl groups and tryptophane residues of CK decreased during the interaction of IM with HRP-H2O2. Other sulfhydryl enzymes, including alcohol dehydrogenase and glyceraldehyde-3-phosphate dehydrogenase, were also readily inactivated during the interaction with HRP-H2O2. Sulfhydryl enzymes seem to be very sensitive to IM activated by HRP-H2O2.

Aggregation of creatine kinase during refolding and chaperonin-mediated folding of creatine kinase

The course of refolding and reactivation of urea-denatured creatine kinase (ATP; creatine N-phosphotransferase, EC 2.7.3.2) has been studied in the absence and presence of molecular chaperonin GroEL. The enzyme was denatured in Tris--HCl buffer containing 6 M urea for 1 h. In the refolding studies, the denatured enzyme was diluted 60-fold into the same buffer containing GroEL or not for activity, turbidity, fluorescence measurements and polyacrylamide gel electrophoresis. The results show that the reactivation process is dependent of creatine kinase concentration in the concentration range 2.5--4 microM. The levels of activity recovery decrease with increasing enzyme concentration because of the formation of wrong aggregates. The molecular chaperonin GroEL can bind the refolding intermediate of creatine kinase and thus prevent the formation of wrong aggregates. This intermediate is an inactive dimeric form that is in a conformation resembling the 'molten globule' state.

Inactivation of rabbit muscle creatine kinase by reversible formation of an internal disulfide bond induced by the fungal toxin gliotoxin

The biological activity of gliotoxin is dependent on the presence of a strained disulfide bond that can react with accessible cysteine residues on proteins. Rabbit muscle creatine kinase contains 4 cysteines per 42-kDa subunit and is active in solution as a dimer. Only Cys-282 has been identified as essential for activity. Modification of this residue results in loss of activity of the enzyme. Treatment of creatine kinase with gliotoxin resulted in a time-dependent loss of activity abrogated in the presence of reducing agents. Activity was restored when the inactivated enzyme was treated with reducing agents. Inactivation of creatine kinase by gliotoxin was accompanied by the formation of a 37-kDa form of the enzyme. This oxidized form of creatine kinase was rapidly reconverted to the 42-kDa species by the addition of reducing agents concomitant with restoration of activity. A 1:1 mixture of the oxidized and reduced monomer forms of creatine kinase as shown on polyacrylamide gel electrophoresis was equivalent to the activity of the fully reduced form of the enzyme consistent with only one reduced monomer of the dimer necessary for complete activity. Conversion of the second monomeric species of the dimer to the oxidized form by gliotoxin correlated with loss of activity. Our data are consistent with gliotoxin inducing the formation of an internal disulfide bond in creatine kinase by initially binding and possibly activating a cysteine residue on the protein, followed by reaction with a second neighboring thiol. The recently published crystal structure of creatine kinase suggests the disulfide is formed between Cys-282 and Cys-73.

Inactivation of creatine kinase by Adriamycin during interaction with horseradish peroxidase

Oxidative damage of creatine kinase (CK) induced by Adriamycin((R)) (ADM) with peroxidase was investigated using horseradish peroxidase (HRP). ADM oxidatively inactivated CK during its interaction with HRP in the presence of H(2)O(2) (HRP-H(2)O(2)). The red color of ADM was lost during oxidation by HRP-H(2)O(2). Adding catalase stopped the color change of ADM induced by HRP-H(2)O(2), indicating that ADM was oxidized by HRP complex I or II. CK was inactivated readily, even when it was added to the reaction mixture containing colorless ADM. Some sulfhydryl groups of CK, which have an important role in its enzyme activity, were very sensitive to ADM activated by HRP-H(2)O(2), suggesting that inactivation of CK is due to oxidation of SH groups at the active center. Presumably, oxidative ADM quinone is involved dominantly in the inactivation of CK. Among the anthracycline drugs tested in this study, only ADM and epirubicin caused inactivation of CK and alcohol dehydrogenase and loss of the red color during oxidation by HRP-H(2)O(2).

Free radical induced inactivation of creatine kinase: sites of interaction, protection, and recovery

The study aims at a clarification of the oxidative damage of creatine kinase isoenzymes by X-ray-induced water radiolysis. The radical species generated by this method (under appropriate conditions) are similar to those discussed in the context of mitochondrial energy metabolism. The decay of the enzyme activity is accompanied by a strong decrease of the number of accessible SH groups and by a reduction of the endogenous tryptophan fluorescence. Free radical effects are diminished if irradiation is carried out in the presence of 2-mercaptoethanol. Partial recovery of the activity (repair) is observed if 2-mercaptoethanol is added after irradiation. The experiments suggest a twofold importance of thiol reagents (RSH): to reduce the concentration of free radicals by scavenger reactions and to modify the inactivation mechanism in such a way that efficient repair of enzyme damage may be achieved. Cysteine 282 of MM-CK (Cys-278 in the case of Mi-CK) seems to play a crucial role in this respect. Blockage of the SH group of cysteine 282 by oxidized glutathione effectively protects the enzyme against inactivation by NO(*)(2) radicals. In the absence of nitrogen dioxide and of thiol reagents, however, inactivation seems to proceed via a less specific mechanism involving additional targets of the enzyme.

Reactivation and refolding of a partially folded creatine kinase modified by 5,5'-dithio-bis(2-nitrobenzoic acid)

Creatine kinase with its thiol groups modified by 5, 5'-dithio-bis(2-nitrobenzoic acid) has been shown to be partially folded in a monomeric state using fluorescence, circular dichroism, proteolysis, and size exclusion chromatography studies. In the presence of DTT, the partially folded modified creatine kinase can be reactivated and refolded following a biphasic course, suggesting the existence of a monomeric intermediate during the refolding of CK. The results provide evidence for our previously suggested model of the refolding pathway of urea-denatured creatine kinase.

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.

The isoenzyme-diagnostic regions of muscle-type creatine kinase, the M-260 and M-300 box, are not responsible for its binding to the myofibrillar M-band

Muscle-type creatine kinase is known for its unique interaction with the myofibrillar M-band, but the molecular origin for this structural relationship is not well understood. A systematic sequence comparison between the highly homologous cytosolic isoforms, muscle-type and brain-type creatine kinase, yielded two isoenzyme-specific regions in the muscle-type creatine kinases, the M-260 box (residues 258-270) and the M-300 box (residues 300-315). These particular regions were conspicuous for the specific interaction of this CK isoenzyme, but not of brain-type creatine kinase, with the sarcomeric M-band. In situ diffusion assays with fluorescently labeled native, as well as mutated muscle-type creatine kinase variants, were used to study by laser confocal microscopy their association with the M-band of chemically skinned muscle fibers. Neither a set of charge mutants of the M-260 box and/or the M-300 box nor a hybrid construct of both isoforms with the entire C-terminal region derived from the brain-type isoform showed any significant alteration in the in situ M-band-binding properties when compared to the wild-type form of muscle-type creatine kinase. This indicates that in the intact protein of muscle type creatine kinase, these C-terminal isoenzyme-specific regions are not important for M-band interaction and that the actual M-band interaction domain(s) lay mostly within the N-terminal half of the molecule. The highly conserved motives (M-260 box and M-300 box) may serve an isoenzyme-specific purpose yet to be identified.

Purification, characterization, and hydrodynamic properties of arginine kinase from gulf shrimp (Penaeus aztecus)

Arginine kinase from the tail muscle of the Gulf shrimp (Penaeus aztecus) was purified to apparent homogeneity, using a rapid, high-yield method. The protein exhibits a molecular weight of 40 kDa according to the methods of gel filtration and gel electrophoresis in sodium dodecyl sulfate, also indicating that arginine kinase from shrimp is a monomer. The amino acid content of arginine kinase from shrimp is similar to arginine kinases from several species and to creatine kinase from rabbit muscle. Arginine kinase derivatized at the reactive sulfhydryl with 2-(4'-(iodoacetamido)anilino)naphthalene-6-sulfonic acid exhibits significant changes in fluorescence anisotropy only in the presence of the guanidino substrate and the so-called "dead-end complex" containing arginine + MgADP. Several compounds structurally similar to arginine, e.g., ornithine do not interact with arginine kinase, suggesting a narrow specificity for substrate binding. The most suitable description of the decay of the fluorescence of arginine kinase derivatized with 5-[(((acetyl)-amino)ethyl)amino]naphthalene-1-sulfonate (AEDANS-AK), from among discrete and distributed models, is a triple exponential discrete decay. The presence of the dead-end complex only marginally increases the rate of decay, but significantly shifts the magnitude of the preexponentials (amplitudes) between the two major decay components. One interpretation of these results is that multiple conformational isomers may occur, in which the relative concentrations are dependent upon the presence of the dead-end complex. Measurement of the time-dependent anisotropy decay of AEDANS-AK reveals a two-term decay law with rotational correlation times of 0.88 and 15.2 ns. The slower component is close to the theoretical value of 16.7 ns for an isotropic rotator of the molecular mass of arginine kinase. This finding suggests that the overall conformation of arginine kinase may differ considerably from the prolate ellipsoidal subunits of the functionally analogous creatine kinase.

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.

Anabolic effects of estrogen and parathyroid hormone on skeletal tissues: the use of creatine kinase B activity as a response marker

The rapid stimulation of the specific activity of the brain type isozyme of creatine kinase (CK BB) is an almost universal marker of cell stimulation. We have studied its stimulation in skeletal-derived cells and shown that the increase in its activity is closely correlated with the biochemical parameter of cell proliferation - [(3)thymidine incorporation into DNA - and with the morphological parameters of bone growth, increase in thickness of cortical bone and of the number of cells in the proliferating zone of the epiphyseal growth plate. We have used the increase in CK activity to demonstrate sex specific stimulation of diaphyseal bone, exclusively by estrogens in females and by androgens in males, and the dependence of sex steroid stimulation on an adequate level of vitamin D. After finding that parathyroid hormone can act as a mitogen via a phospholipase-C-phosphoinositide turnover pathway, we collaborated with colleagues at the GBF in Braunschweig to find that mid-region fragments of PTH could act exclusively as mitogens, without stimulating cAMP production leading to bone resorption. hPTH (28-48) variants designed to be resistant to proteolysis were efficient in stimulating CK specific activity in vitro and in vivo and increased cortical bone thickness and the number of proliferating epiphyseal cartilage cells in rat long bones. These results are put into an historical context and compared with recent studies, in this short, selective review.

Conformational changes of arginine kinase induced by photochemical release of nucleotides from caged nucleotides--an infrared difference-spectroscopy investigation

The conformations of arginine kinase (AK) in AK x Mg x ADP, AK x Mg x ATP, AK x Mg x ADP x NO3-, AK x Mg x ADP x Arg and AK x Mg x ADP x NO3- x Arg complexes were investigated by measuring their reaction-induced infrared difference spectra (RIDS). The photochemical release of ATP from ATP[Et(PhNO2)] and of ADP from ADP[Et(PhNO2)] produced distinct RIDS of AK complexes, suggesting that binding of ADP and ATP promoted different structural alterations of the enzyme active-site. Small infrared changes in the amide-I region were observed, indicating that about 5-10 amino acid residues were involved in the nucleotide-binding site. These infrared changes were due to the structural alteration of the peptide backbone caused by the nucleotide-binding and to the coupling effects between the nucleotide-binding site and the other substrate (Arg or NO3-)-binding site. ATP binding to AK (as well as ADP-binding to AK in the presence of NO3-) induced protonation of a carboxylate group of Asp or Glu, as evidenced by the appearance of the 1733-cm(-1) band, which was not observed with the AK x Mg x ADP, AK x Mg x ADP x Arg and AK x Mg x ADP x NO3- x Arg complexes. The RIDS of the AK x Mg x ADP x NO3- x Arg complex showed new infrared bands at 1622 cm(-1) (negative) and at 1613 cm(-1) (positive), which were not seen in the RIDS of other complexes (without NO3- or/and Arg). In the transition-state-analog complex of AK, no protonation of the carboxylate residue (Asp or Glu) was observed, and the binding site of NO3- or the gamma-phosphate group of nucleotide was altered.

Creatine kinase is the main target of reactive oxygen species in cardiac myofibrils

Reactive oxygen species (ROS) have been reported to alter cardiac myofibrillar function as well as myofibrillar enzymes such as myosin ATPase and creatine kinase (CK). To understand their precise mode and site of action in myofibrils, the effects of the xanthine/xanthine oxidase (X/XO) system or of hydrogen peroxide (H2O2) have been studied in the presence and in the absence of phosphocreatine (PCr) in Triton X-100-treated cardiac fibers. We found that xanthine oxidase (XO), with or without xanthine, induced a decrease in maximal Ca(2+)-activated tension. We attributed this effect to the high contaminating proteolytic activity in commercial XO preparations, since it could be prevented a protease inhibitor, phenylmethylsulfonyl fluoride (PMSF), and it could be mimicked by trypsin. In further experiments, XO was pre-treated with 1 mmo1/L PMSF. Superoxide anion production by the X/XO system, characterized by electron paramagnetic resonance spin-trapping technique, was not altered by PMSF. A slight increase in maximal force was then observed either with X/XO (100 mumol/L per 30 mIU/mL) or H2O2. pMgATP-rigor tension relationships have been established in the presence and in the absence of PCr to separate the effects of ROS on myosin ATPase and myofibrillar-bound CK. In the absence of PCr, pMgATP50, the pMgATP necessary to induce half-maximal rigor tension, was reduced from 5.03 +/- 0.17 (n = 21) to 4.22 +/- 0.22 (n = 4) after 25 minutes of incubation in the presence one of 30 mIU/mL. XO and 100 mumol/L xanthine or to 4.04 +/- 0.1 (n = 11) after incubation in the presence of 2.5 mmol/L H2O2. The ROS effects were partially prevented or antagonized by 1 mmol/L dithiothreitol. No effect was observed on pMgATP50 when PCr was absent. pCa-tension relationships have been evaluated to assess the effects of ROS on active tension development. Incubations with H2O2 induced on increase in Ca2+ sensitivity and resting tension when MgATP was provided through myofibrillar CK (PCr and MgADP as substrates) but not when MgATP was added directly. These results suggest that myofibrillar CK was inhibited by ROS. Active stiffness and the time constant of tension changes after quick stretches applied to the fibers were dose-dependently increased by H2O2 only in the presence of PCr. In addition, myofibrillar CK but not myosin ATPase enzymatic activity was depressed after incubation with either ROS. These results suggest that ROS mainly alters CK in myofibrils, probably by the oxidation of its essential sulfhydryl groups. Such CK inactivation results in a decrease in the intramyofibrillar ATP-to-ADP ratio. The effects of ROS on cytosolic and bound CKs may take part in the overall process of myocardial stunning after cardiac ischemia and reperfusion.

Unfolding, conformational change of active sites and inactivation of creatine kinase in SDS solutions

It has been reported that inactivation occurs before noticeable conformational change can be detected during denaturation of creatine kinase (ATP: creatine N-phosphotransferase, EC 2.7.3.2) and other enzymes by guanidinium chloride or urea. Therefore, Tsou suggested that enzyme active sites may display more conformational flexibility than the enzyme molecules as a whole [Tsou (1986) Trends Biochem. Sci. 11, 427-429; Tsou (1993) Science 262, 380-381]. In this study, the conformational change of the active site, the unfolding of the whole molecule and the inactivation of creatine kinase in solutions of different concentrations of SDS are compared. The results show that, at low SDS concentrations, the conformational change of the active site and inactivation of the enzyme occur to nearly the same extent. However, both of these changes occur at much lower concentrations of SDS than required to significantly unfold the enzyme molecule. The rates of conformational changes of enzyme active sites are markedly faster than those of inactivation. However, at the same SDS concentration, both the inactivation rate and the rate of the active site conformational change are much faster than that of the unfolding of the enzyme molecule as a whole. The above results provide direct evidence of the flexibility of the active site of creatine kinase.

Creatine kinase equilibration follows solution thermodynamics in skeletal muscle. 31P NMR studies using creatine analogs

The hypothesis tested was whether creatine kinase (CK) equilibrates with its substrates and products in the cytosol as if in solution. We used the creatine analogs cyclocreatine (cCr) or beta-guanidopropionate (beta GPA) to test if mass action ratios (gamma) for CK in muscle could be predicted from combined equilibrium constants (Kcomb) measured in solutions mimicking the intracellular environment. Mice were fed cCr or beta GPA and their muscles assayed for substrates and products of the CK reaction by 31P NMR spectroscopy and high performance liquid chromatography. After three weeks of feeding, gamma was indistinguishable from Kcomb in cCr-treated muscles demonstrating both PCr/Cr and phospho-analog/analog must have equilibrated with a constant and uniform cellular ATP/ADP ratio. In beta GPA-treated muscles, gamma was smaller than Kcomb due to a higher content of muscle beta GPA. Feeding beta GPA for 9-12 weeks resulted in a closer agreement between Kcomb and gamma, suggesting ATP/ADP ratios are not uniform within the muscle perhaps due to transient metabolic stress in some cells. From this analysis it follows that calculation of free ADP from the CK equilibrium for a heterogeneous population of cells with respect to total Cr and ATP content is correct only if chemical potentials of these cells are uniform.

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.

Endomyocardial gene expression during development of pacing tachycardia-induced heart failure in the dog

Selective and specific changes in gene expression characterize the end-stage failing heart. However, the pattern and relation of these changes to evolving systolic and diastolic dysfunction during development of heart failure remains undefined. In the present study, we assessed steady-state levels of mRNAs encoding a group of cardiac proteins during the early development of left ventricular dysfunction in dogs with pacing-induced cardiomyopathy. Corresponding hemodynamic assessments were made in the conscious state in the same animals and at the same time points at baseline, after 1 week of ventricular pacing, and at the onset of clinical heart failure. Systolic dysfunction dominated after 1 week of pacing, whereas diastolic dysfunction was far more pronounced with the onset of heart failure. Atrial natriuretic factor mRNA was undetectable in 7 of 12 hearts at baseline but was expressed in all hearts at 1 week (P < .01 by chi 2 test), and it increased markedly with progression to failure (P = .05). Creatine kinase-B mRNA also rose markedly with heart failure (P < .01). Levels of mRNA encoding beta-myosin heavy chain, mitochondrial creatine kinase, phospholamban, and sarcoplasmic reticulum Ca(2+)-ATPase did not significantly change from baseline, despite development of heart failure. Additional analysis to determine if these mRNA changes were related to the severity of diastolic or systolic dysfunction revealed that phospholamban mRNA decreased in hearts with larger net increases in end-diastolic pressure (+19.2 +/- 1.9 mm Hg) compared with those hearts in which it did not change (+4.0 +/- 4.9, P < .02).(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of the catalytic site of creatine kinase by site-directed mutagenesis

Site-directed mutagenesis was used to alter the amino-acid residues at the presumed catalytic site Cys-283 and ATP binding site Asp-340 of human creatine kinase B cDNA. In addition, a highly conserved arginine residue, Arg-292, was also mutated. Transfection of 0.1 to 1 microgram of recombinant plasmid into COS cells produced increasing creatine kinase activity in the cell lysate. The expression of mutant Cys283-Tyr and Cys283-Ser resulted in complete abolition of homodimer BB isoform enzymatic activity without alteration of the capacity for dimerization. Expression of mutants Arg292-His, Arg292-Leu, and Arg292-Gln produced non-functional homodimers, whereas expression of mutant Arg292-Lys produced a homodimer with enzymatic activity that was 42% of the enzymatic activity of the wild type. Expression of the Asp340-Glu mutant creatine kinase did not alter enzyme activity as compared to the wild type. Following heterodimerization, there was inhibition of the normal subunit by the mutant subunit, for both the BB and the MB dimer. The results showed residues Cys-283 and Arg-292 are essential for enzyme catalysis. The best fit model for the dimer is one in which there is close apposition of the two catalytic sites. The interaction of the individual subunits during dimerization provides a molecular approach for dominant negative modulation of the creatine kinase isozyme system in future genetic manipulative experiments.

Chemical synthesis of bispecific monoclonal antibodies: potential advantages in immunoassay systems

To date, the applications of bispecific antibodies in immunoassay and immunocytochemical procedures have been directed at uniting two different biomolecules through the binding of epitopes on each respective substance. In this study, bispecific antibodies were constructed in which both binding sites were directed to two different epitopes of the same target molecule. Two types of bispecific antibody were constructed; a bivalent bispecific monoclonal antibody and multivalent bispecific polymers. The binding characteristics of each were investigated for changes in specificity and binding strength relative to 1:1 mixtures of parent antibodies. A bivalent bispecific antibody (BBA) was synthesised by the method of Glennie et al. (1985) from monoclonal antibodies recognising the 'M' or 'B' units of creatine kinase (CKMB). The BBA had enhanced specificity for CKMB with diminished recognition of CKMM and CKBB. A less tedious method of producing bispecific antibody involving heterobifunctional cross-linkage was used to produce multivalent bispecific antibodies (MBAs). Certain MBAs constructed to bind 'M' and 'B' units of CKMB demonstrated enhanced specificity and affinity for CKMB. MBAs were also produced to opposite ends of the 39 amino acid peptide adrenocorticotrophic hormone (ACTH). One of these demonstrated an enhanced affinity of 41-fold. We conclude that while conventional synthesis of bispecific bivalent antibodies is not a practical proposition for immunoassay development, antibodies with similar advantages can be produced with a simple method using the heterobifunctional cross-linker. The production of certain bispecific antibody combinations appears to enhance the formation of antibody-antigen matrices conferring higher binding affinities than can be achieved with an antibody mixture alone.

Immunofluorescent analysis of creatine kinase in cultured astrocytes by conventional and confocal microscopy: a nuclear localization

The subcellular localization of creatine kinase (CK) was examined in primary cultures of astrocytes with immunofluorescent labeling methods and detection by both standard fluorescence microscopy and confocal laser-scanning microscopy. With conventional microscopy, the pattern of CK staining was uniform throughout the cell cytoplasm and appeared to stain the nuclear region intensely. Staining of CK in the nuclear region co-localized with the DNA-specific Hoechst nuclear stain. CK produced a diffuse cytoplasmic staining pattern that was different from the staining pattern produced by the cytoskeletal proteins glial fibrillary acidic protein and tubulin, both of which showed a filamentous cytoskeletal network that excluded the nucleus. To examine the structural details of CK in the nuclear region, serial optical sections were taken through the cell monolayer with a confocal microscope. The cells were immunostained for CK, and the CK-staining pattern was compared with the staining pattern produced by propidium iodide, which is specific for DNA in RNase-treated samples and stains total nucleic acid in untreated samples. CK staining was present within the nucleus in each section taken through the monolayer. The nucleolus did not stain for CK. The pattern of CK staining in the nucleus (and cytoplasm) was distinctly different from the staining pattern of either DNA or total nucleic acid. Nuclear CK appeared to have a granular, particulate pattern, which is suggestive of a nucleoplasmic distribution.

Regulation of expression of M, B, and mitochondrial creatine kinase mRNAs in the left ventricle after pressure overload in rats

Pressure overload of the left ventricle induces synthesis of creatine kinase isoenzymes. To determine whether this response is associated with an altered pattern of creatine kinase gene expression, we induced arterial hypertension in rats by suprarenal aortic banding. After 4 days, left ventricular myocardium from hypertensive (n = 7) and normotensive, sham-operated (n = 5) rats was analyzed for isoenzyme activities by chromatography; M and B creatine kinase subunit protein by Western blot; and M, B, and mitochondrial creatine kinase mRNA by Northern blot. Although total creatine kinase activity increased in hypertensive (1,096 +/- 214 IU/g left ventricle) compared with normotensive rats (648 +/- 81 IU/g left ventricle, p less than 0.01), the relative proportions of the cytoplasmic and mitochondrial isoenzymes did not change. The mass of M and B subunits increased 1.9- and 2.7-fold, respectively, in hypertensive compared with control rats. Similarly, the mRNA for M and B subunits as well as mitochondrial creatine kinase increased 2.6-, 1.6-, and 1.8-fold, respectively, in hypertensive rats compared with control rats. Thus, increased energy requirements in acute pressure overload are met by generalized induction of creatine kinase mRNA and subunit protein and not by an isoenzyme switch.

ATP binding site of mitochondrial creatine kinase. Affinity labelling of Asp-335 with C1RATP

The ATP binding site of mitochondrial creatine kinase from chicken heart has been studied by modifying the purified enzyme with a 14C-labelled ATP analogue, C1RATP, in which the reactive label was covalently bound to the gamma-phosphate group of ATP. The modified enzyme was digested by pepsin, and a single radioactive nonapeptide was isolated by HPLC. Amino acid analysis and direct sequence determination revealed that the isolated peptide corresponds to amino acids 335-343 within the C-terminal region of Mi-CK, this peptide being highly preserved throughout evolution. Asp-335 is very likely the site of modification by C1RATP. The specificity of the ATP analogue for the active site of creatine kinase was demonstrated by the inhibition of the enzymatic activity of Mi-CK by C1RATP and by the prevention of this inhibition bij ADP.

Monoclonal antibody studies suggest a catalytic site at the interface between domains in creatine kinase

We have located the epitopes recognized by four different monoclonal antibodies which bind to partially unfolded creatine kinase (CK) (ATP: creatine N-phosphotransferase, EC 2.7.3.2) but not to the native enzyme. The epitopes appear to be buried within the CK structure in its native, proteinase-resistant, state. When the epitopes are made accessible to antibody by mild denaturation, CK becomes enzymically-inactive and can be cleaved by proteinase V8 into two large fragments which retain the epitopes and may represent domains. Epitopes on each V8 fragment are associated with highly conserved sequences and are brought physically close to the active site of the enzyme during the later stages of CK refolding and reactivation. The results suggest a catalytic site formed at the interface between two domains which carry the epitopes on their interacting surfaces. Separation of loosely associated domains before or during immunization may account for the origin of antibodies against buried epitopes.

Tissue-specific distribution and developmental regulation of M and B creatine kinase mRNAs

To characterize the tissue-specific distribution and developmentally regulated expression of M and B creatine kinase mRNA in rats, total cellular RNA was isolated from adult rat tissues and from skeletal muscle, heart, brain and intestine at selected stages of development. Northern blots were prepared and hybridized with M and B subunit-specific probes derived from the 3'-untranslated region. M creatine kinase mRNA was expressed abundantly in heart and skeletal muscle, and less abundantly in lung. B creatine kinase mRNA was found in all tissues examined except liver and was abundant in brain, heart and intestine. The developmentally regulated expression of M and B creatine kinase mRNA was determined in skeletal muscle, heart, brain and intestine. The developmental program of B creatine kinase mRNA was different for each tissue examined. During development, M creatine kinase mRNA was up-regulated in both heart and skeletal muscle with a different regulatory program. This resulted in replacement of B mRNA by M mRNA as the predominant species at an earlier developmental stage in heart when compared to skeletal muscle.

Manipulating the intracellular environment of hippocampal slices: pH and high-energy phosphates

The intracellular energetic environment of rat hippocampal slices was manipulated by bolstering ATP levels following the addition of adenosine to the incubation medium, or by manipulating intracellular pH. Addition of 8 mM adenosine to the incubation medium increased total tissue adenylate and ATP content, but did not prolong electrical function during anoxia. Further, it resulted in long-lasting alterations in normoxic evoked responses. Intracellular pH (pHi) was changed by manipulating the bicarbonate/CO2 ratio of the incubation medium, or by adding amiloride, a hydrogen/sodium antiport blocker. Estimates of intracellular pH using the creatine kinase equilibrium agree with those obtained by Neutral red scanning spectrophotometry in control conditions. However, only Neutral red indicated an acidification with amiloride treatment, while the creatine kinase equilibrium was preferentially affected by hypercapnia, suggesting the presence of at least two pH compartments in hippocampal brain slices. These manipulations cannot be carried out easily in vivo, and provide a means of determining the importance of metabolic changes on neural function during anoxia.

Only one of the two interconvertible forms of mitochondrial creatine kinase binds to heart mitoplasts

When analyzed by cellulose acetate electrophoresis, solubilized pig or rabbit heart mitochondrial creatine kinase is shown to exist under two distinct forms. The less cathodic one (form 1) is a dimer and the other having a higher cathodic mobility (form 2) has a molecular weight of about 350,000. The latter form can be converted into the former by incubation at alkaline pH or when the enzyme forms a reactive or an abortive complex with its substrates. This conversion is a reversible phenomenon and is not due to proteolysis. When rabbit heart mitoplasts are treated with the creatine kinase releasing agents, the enzyme is always solubilized as its form 2 and conversion to form 1, when it occurs, always take place after solubilization. Form 2 is also the only form which can be bound to pig or rabbit mitoplasts. Thus form 2 may be the actual form associated with heart mitochondria in vivo.

Innervation is required to stabilize and amplify creatine kinase activity in regenerated extensor digitorum longus muscles of rats

Neural control of creatine kinase (CK, adenosine 5'-triphosphate creatine phosphotransferase: EC 2.7.3.2) was investigated by measuring enzymatic activity and isoenzymatic representation of CK in extensor digitorum longus (EDL) muscles of adult rats during and after regeneration. Experimental models were ischemized EDLs, reversibly or permanently denervated. Results showed that, during regeneration, CK in muscle fibers was likewise modified in both reversibly and permanently denervated EDLs. After regeneration a clear dichotomy was observed between the regenerated EDLs which were innervated and recovering CK activity, and those in which innervation was prevented and were rapidly losing activity. Further to investigate the neural influence on CK turnover, merely denervated age-matched EDLs were analysed and found to lose CK activity rapidly. The major conclusions are that during regeneration muscle CK is autonomously expressed, but following regeneration neural influence becomes an absolute requirement for stabilization and amplification of CK.

Detection of cerebral injury after total circulatory arrest and profound hypothermia by estimation of specific creatine kinase isoenzyme levels using monoclonal antibody techniques

New 2-site labeled monoclonal antibody techniques were used to measure serially plasma levels of brain-type creatine kinase (CK-BB), heart-type creatine kinase (CK-MB) and muscle-type creatine kinase (CK-MM) during a 20-hour postoperative period in 24 infants after deep hypothermia and total circulatory arrest used in pediatric cardiac surgery. A control group of 7 children undergoing cardiovascular procedures without extracorporeal circulation or circulatory arrest also were studied. There were marked increases in CK-MB and CK-BB levels in the circulatory arrest group but not in the closed group. CK-BB increased from 3.2 +/- 0.5 to 27 +/- 10 ng/ml and CK-MB from 5.9 +/- 2.1 to 137 +/- 12 ng/ml. The CK-MM concentrations increased from 299 +/- 91 and 194 +/- 49 ng/ml to 1,220 +/- 274 and 1,322 +/- 142 ng/ml in the closed and circulatory arrest groups, respectively. Peak levels of CK-MB and CK-BB occurred an average of 133 and 127 minutes, respectively, after reperfusion. The half-time of CK-BB differed significantly from that of CK-MB (149 +/- 15 vs 359 +/- 20 minutes). The arrest time had a more marked effect on CK-BB concentration than on CK-MB and CK-MM concentrations. Arteriointernal jugular venous concentration differences were consistently negative for CK-BB in the circulatory arrest group, but not for CK-MM and CK-MB.(ABSTRACT TRUNCATED AT 250 WORDS)

The complete nucleotide sequence of canine brain B creatine kinase mRNA: homology in the coding and 3' noncoding regions among species

To define the structure of canine B creatine kinase, clones were isolated from a library prepared from dog brain mRNA and constructed in the vector lambda gt11. The entire coding portion, the complete 3' nontranslated region, and 43 bp of the 5' noncoding region are reported. Comparison of the predicted amino acid sequence of canine B creatine kinase with the sequence of canine M creatine kinase shows 81% identity. When compared to cDNAS encoding B creatine kinase isolated form other species unusual and striking nucleotide sequence identity in the 3' noncoding region is present. Moreover, two B creatine kinase clones (BCK2 and BCK38) demonstrate microheterogeneity within the 3' nontranslated region indicating variable processing of B creatine kinase pre-mRNA or the existence of multiple genes encoding canine B creatine kinase.