Kinetic properties and functional role of creatine phosphokinase in glycerinated muscle fibers--further evidence for compartmentation

Effects of free radicals on cytosolic creatine kinase activities and protection by antioxidant enzymes and sulfhydryl compounds

The main purpose of this study was to investigate the effect of free radicals and experimental diabetes on cytosolic creatine kinase activity in rat heart, muscle and brain. Hydrogen peroxide decreased creatine kinase activity in a dose dependent manner which was reversed by catalase. Xanthine/xanthine oxidase, which produces superoxide anion, lowered the creatine kinase activity in the same manner whose effect was protected by superoxide dismutase. N-acetylcysteine and dithiothreitol also significantly ameliorated the effect of Xanthine/xanthine oxidase and hydrogen peroxide. Experimental diabetes of twenty-one days (induced by alloxan), also caused a similar decrease in the activity of creatine kinase. This led us to the conclusion that the decrease in creatine kinase activity during diabetes could be due to the production of reactive oxygen species. The free radical effect could be on the sulfhydryl groups of the enzyme at the active sites, since addition of sulfhydryl groups like N-acetylcysteine and dithiothreitol showed a significant reversal effect.

Contractile and metabolic effects of increased creatine kinase activity in mouse skeletal muscle

The effects of increased expression of creatine kinase (CK) in skeletal muscle were studied in control and transgenic animals homozygous for expression of the B subunit of CK. CK activity was 47% higher in transgenic gastrocnemius muscle. The CK activity was distributed as follows: 45 +/- 1% MM dinner, 31 +/- 4% MB dimer, and 22 +/- 5% BB dimer. No significant differences in metabolic or contractile proteins were detected except for a 22% decrease in lactate dehydrogenase activity and a 9% decrease in adenylate kinase activity. The only significant effect in contractile activity was that the rise time of a 5-s isometric contraction was 28% faster in the transgenic muscle. 31P nuclear magnetic resonance (NMR) spectra were obtained from control and transgenic muscles during mechanical activation, and there were no NMR measurable differences detected. These results indicate that a 50% increase in CK activity due to expression of the B subunit does not have large effects on skeletal muscle metabolism or contractile function. Therefore, control muscle has sufficient CK activity to keep up with changes in cellular high-energy phosphates except during the early phase of intense contractile activity.

Myofibrillar creatine kinase and cardiac contraction

This article is a review on the organization and function of myofibrillar creatine kinase in striated muscle. The first part describes myofibrillar creatine kinase as an integral structural part of the complex organization of myofibrils in striated muscle. The second part considers the intrinsic biochemical and mechanical properties of myofibrils and the functional coupling between myofibrillar CK and myosin ATPase. Skinned fiber studies have been developed to evidence this functional coupling and the consequences for cardiac contraction. The data show that creatine kinase in myofibrils is effective enough to sustain normal tension and relaxation, normal Ca sensitivity and kinetic characteristics. Moreover, the results suggest that myofibrillar creatine kinase is essential in maintaining adequate ATP/ADP ratio in the vicinity of myosin ATPase active site to prevent dysfunctioning of this enzyme. Implications for the physiology and physiopathology of cardiac muscle are discussed.

Changes in creatine kinase M localization in acute ischemic myocardial cells. Immunoelectron microscopic studies

To clarify the changes in creatine kinase M localization along with the progress of myocardial ischemia, immunoelectron microscopic studies were performed using rabbit anti-canine creatine kinase M Fab'-horseradish peroxidase conjugate in 21 dogs. Myocardial ischemia was induced by occlusion of the left anterior descending coronary artery for 15 (n = 5), 30 (n = 5), 60 (n = 5), or 180 (n = 4) minutes. Two dogs were used as normal controls. As we have already demonstrated, most creatine kinase M in normal myocardial cells was localized over the entire A band in association with the thick filament, suggesting that creatine kinase in this region (A-band creatine kinase) was the enzyme coupled with myosin ATPase. After 15 minutes of ischemia, creatine kinase M showed only minimal changes in its location, indicating that A-band creatine kinase still has the ability to couple with myosin ATPase (reversible injury). However, after 30 minutes of ischemia, A-band creatine kinase diffused markedly to the I band (transitional phase), and after 60 minutes of ischemia, it leaked out to extracellular spaces (irreversible injury). After 180 minutes of ischemia, most A-band creatine kinase disappeared from the myocardial cells (coagulation necrosis). These features of creatine kinase M localization seemed to reflect each stage of ischemic cell injury. We conclude that myocardial ischemia results in a dissociation of creatine kinase molecules from the thick filament, which leads the energy transport system to destruction.

Decrease in heart mitochondrial creatine kinase activity due to oxygen free radicals

This study was undertaken to examine the effects of oxygen free radicals on mitochondrial creatine kinase activity in rat heart. Xanthine plus xanthine oxidase (superoxide anion radical generating system) reduced mitochondrial creatine kinase activity both in a dose- and a time-dependent manner. Superoxide dismutase showed a protective effect on depression in creatine kinase activity due to xanthine plus xanthine oxidase. Hydrogen peroxide inhibited creatine kinase activity in a dose-dependent manner, this inhibition was protected by the addition of catalase. In order to understand the detailed mechanisms by which oxygen free radicals inhibit mitochondrial creatine kinase activity, the effects of oxygen free radicals on mitochondrial sulfhydryl groups were examined. Mitochondrial sulfhydryl groups contents were decreased by xanthine plus xanthine oxidase or hydrogen peroxide; this depression in sulfhydryl groups contents was prevented by the addition of superoxide dismutase or catalase. N-Ethylmaleimide (sulfhydryl group reagent) expressed inhibitory effects on the creatine kinase activity both in a dose- and a time-dependent manner; dithiothreitol or cysteine (sulfhydryl group reductant) showed protective effects on the creatine kinase activity depression induced by N-ethylmaleimide. Dithiothreitol or cysteine also blocked the depression of mitochondrial creatine kinase activity caused by xanthine plus xanthine oxidase or hydrogen peroxide. These results lead us to conclude that oxygen free radicals may inhibit mitochondrial creatine kinase activity by modifying sulfhydryl groups in the enzyme protein.

Cardiac myofibrillar creatine kinase Km is not influenced by contractile protein binding

Subcellular microcompartmentation underlies the proposed phosphorylcreatine shuttle mechanism in mammalian cardiac tissue. In mitochondria, CK coupling to oxidative phosphorylation via adenine nucleotide translocase decreases the Km for ATP and suggests both a functional and physical integration. In the present studies, substrate Km of myofibrillar CK was unaltered when determined in the intact, native state or after removal from the myofibril. In contrast to mitochondria, close spatial proximity between cardiac myofibrillar CK and ATPase is sufficient to establish phosphorylcreatine shuttle microcompartmentation.

Myofibrillar M-band proteins in rat skeletal muscles during development

The distribution of three myofibrillar M-band proteins, myomesin, M-protein and the muscle isoform of creatine kinase, was investigated with immunocytochemical techniques in skeletal muscles of embryonic, fetal, newborn and four-week-old rats. Furthermore, muscles of newborn rats were denervated and examined at four weeks of age. In embryos, myomesin was present in all myotome muscle fibres of the somites, whereas M-protein was detected only in a small proportion of the myotome muscle fibres and muscle creatine kinase was not detected at all. In fetal and newborn muscles, all fibres contained all three M-band proteins. At four weeks of age, when fibre types (type 1 or slow twitch fibres and type 2 or fast twitch fibres) were clearly discernable, the pattern was changed. Myomesin and muscle creatine kinase were still observed in all fibres, whereas M-protein was present only in type 2 fibres. On the other hand, in muscle fibres denervated at birth all three M-band proteins were still detected. Our results suggest 1) that during the initial stages of myofibrillogenesis expression and incorporation of myomesin into the M-band precede that of M-protein and muscle creatine kinase; 2) that expression and incorporation of all three M-band proteins during fetal development is nerve independent and non coordinated to the expression of different forms of myosin heavy chains, and 3) that the suppression of M-protein synthesis during postnatal development is nerve dependent and reflects the maturation of slow twitch motor units.

The polysome as a terminal for the creatine phosphate energy shuttle

The role of the creatine phosphate shuttle in the energetics of muscle protein synthesis in isolated polysomes, from rat hindlimb muscle, was studied. Triton X-100-treated polysomes, following their centrifugation through a 1 M sucrose gradient, contained 38 mU/mg RNA of bound creatine kinase. In the presence of pH 5 enzyme (obtained from rat liver), 0.5 mM ATP, and 1 microM GTP, amino acid (leucine) incorporation by polysomes in the presence of 8 mM creatine phosphate was twice that in the presence of an exogenous ATP regenerating system of 10 mM phospho(enol)pyruvate and 10 U/ml pyruvate kinase. Since added creatine kinase had no effect on incorporation supported by creatine phosphate it is clear that endogenous creatine kinase allows sufficient regeneration of ATP. These data also suggest that nucleoside diphosphokinase must have been associated with the polysome for phosphate was transferred to GTP from [33P]creatine phosphate, and the specific activities of ATP and GTP increased at equal rates, reaching the specific activity of creatine phosphate at 8 min. We conclude that skeletal muscle polysomes have bound creatine kinase activity and they act as terminals for the creatine phosphate energy shuttle. Creatine phosphate regenerates GTP, probably through an intermediate reaction catalyzed by nucleoside diphosphokinase. This provided an added support for the hypothesis of compartmentation of enzymes and substrates and that the transport form of energy between the mitochondria and energy utilizing sites in muscle is creatine phosphate rather than ATP, which extends the general role of the creatine phosphate energy shuttle.

Phosphorylcreatine shuttle enzymes during perinatal heart development

Mammalian heart development, from the time of weaning until adulthood, is characterized by progressive and significant enhancement in functional performance. Aerobic metabolism and contractile protein ATPase activity increase in parallel with augmented cardiac function. The present studies examined the potential contribution of phosphorylcreatine shuttle enzymes to the developmentally linked alterations in heart performance. Mitochondrial ATPase specific activity was not altered between weanling and adult heart; however, creatine kinase activity was enhanced approximately threefold. Myofibrillar ATPase activity doubled over the developmental time course, while creatine kinase activity increased to an even greater extent. Enhanced myofibrillar ATPase activity was not due to alterations in either calcium sensitivity or ATPase activity measured in purified myosin. Both the mitochondrial and myofibrillar creatine kinase enzyme activities are enhanced during normal heart growth; however, relatively greater enhancement of the myofibrillar component occurs. Thus, enzymatic reactions comprising the phosphorylcreatine shuttle system are dramatically increased during normal heart development. This mechanism deserves consideration as a potentially powerful contributor to enhanced cardiac function during the perinatal period.

Role of creatine kinase in force development in chemically skinned rat cardiac muscle

The influence of phosphocreatine in the presence or absence of MgATP and MgADP was studied in Triton X-100-treated thin papillary muscles and ventricular strips of the rat heart. The pCa/tension relationships, the pMgATP/tension relationships, and the tension responses to quick length changes were analyzed. The results show three major consequences of the reduction of the phosphocreatine concentration in the presence of millimolar concentrations of the MgATP. (a) The resting tension and the maximal Ca2+-activated tension were increased, and the pCa/tension relationship was shifted toward higher pCa values and its steepness was decreased; these effects were enhanced by the inclusion of MgADP. (b) The time constant of tension recoveries after quick stretches applied during maximal activation was increased, while the extent of these recoveries was decreased. (c) The study of pMgATP/tension relationships in low Ca concentrations showed that the decrease in phosphocreatine induced a shift toward higher MgATP values with no changes in maximal rigor tension or the slope coefficient; these effects were increased by the increase in MgADP and were independent of the preparation diameter. Thus, modifications of the apparent Ca sensitivity and resting and maximal tension when phosphocreatine is decreased seem to be due to an increasing participation of rigor-like or slowly cycling cross-bridges spending more time in the attached state. These results suggest that endogenous creatine kinase is able to ensure maximal efficiency of myosin ATPase by producing a local high MgATP/MgADP ratio.

The creatine phosphate energy shuttle--the molecular asymmetry of a "pool"

The creatine phosphate shuttle energy transfer mechanism was postulated on the basis of the hexokinase acceptor theory of insulin action. It proposes that the movement of chemical energy from the mitochondrion to the myofibril is in the form of creatine phosphate. This occurs because there are isozymes of creatine phosphokinase bound to the inner membrane of the sarcosome and to the A band of the myofibril. These isozymes have been shown to act as transducers of energy from ATP to creatine phosphate at the translocase site and from creatine phosphate back to ATP at the myofibrillar compartment. Calculations show that there is no significant amount of transformation of creatine phosphate to ATP in the intervening space between the mitochondrion and the myofibril so that, essentially, transport between the oxidative sites and the contractile apparatus is through the creatine phosphate shuttle. There is also evidence that another terminus for this shuttle is the microsome so that muscle activity tends to increase energy supply for protein synthesis.

Disruption of myofibrillar energy use: dual mechanisms that may contribute to postischemic dysfunction in stunned myocardium

The abnormalities in regional function produced by myocardial ischemia persist after the ischemic episode resolves. Since a close functional coupling exists between myofibrillar creatine kinase and myosin ATPase, a disruption of this coupling could adversely influence myocardial function and might provide a mechanism for the myocardial dysfunction observed. The purpose of the present study was to determine if an alteration in the activity of creatine kinase associated with the myofibril occurs in the postischemic period. Anesthetized open-chest dogs (n = 6) underwent coronary occlusion for 15 minutes, followed by reperfusion for 15 minutes. In reperfused myocardium, adenine nucleotide content was decreased (72 +/- 10% of nonischemic myocardium, p less than 0.05), documenting the presence of previous ischemia. The creatine phosphate content of reperfused myocardium returned to normal, indicating resumption of myocardial energy production. The creatine kinase activity of purified myofibrils isolated from reperfused myocardium was decreased by 17 +/- 7% compared to that of nonischemic myofibrils (p less than 0.03). In addition, the free adenosine diphosphate concentration in reperfused myocardium was calculated to be 96 microM and was less than the Km of adenosine diphosphate determined for myofibrillar creatine kinase (105 microM). The results suggest two putative mechanisms for disruption of energy use in postischemic myocardium: decreased creatine kinase activity associated with the myofibril, and limitation of substrate necessary for maximal creatine kinase activity.

Myokinase and contractile function of glycerinated muscle fibers

Glycerinated rabbit psoas muscle fibers containing native CPK, ATPase, and myokinase activities were used and isometric contraction and relaxation responses to either ADP or ATP + CP or to ATP alone in the presence and absence of P1, P5-di(adenosine-5'-pentaphosphate), a myokinase inhibitor, were compared. In previous (14) work it was shown that CP generated more efficient and faster contraction and relaxation of glycerinated muscle fibers than ATP. The present work deals with the role of myokinase in the differential response of fibers to CP and ATP. Inhibition of the myokinase activity of these fibers caused slight diminution of the rate of contraction at physiological concentrations of ATP. Uninhibited fibers were not able to reach maximum contraction, because the tension began to drop gradually even in the presence of Ca2+. Addition of Ap5A permitted maximum contraction and the ability to stay at the contracted state. In the case of CP + adenosine nucleotides (ATP or ADP), myokinase activity decreased the rate of tension development which was statistically significant after 5-7 sec of contraction. Thus, a higher tension was obtainable when myokinase was inhibited. At high concentration of adenine nucleotides (greater than 2 mM) and in the absence of Ap5A, not only the maximum tension never was reached, but a spontaneous drop in tension was observed before addition of EGTA, as was seen with ATP alone. Relaxation was faster and more complete in the presence of uninhibited myokinase activity except that the ADP was low (125 mM). These observations provide further evidence for a close functional interaction of these three enzymes in the mechanism of contraction and relaxation, giving further support to the notion of the creatine-phosphocreatine energy shuttle.

Role of myofibrillar creatine kinase in the relaxation of rigor tension in skinned cardiac muscle

In the absence of creatine phosphate, MgATP produced relaxation of rigor tension in chemically-skinned right papillary muscles of the rat, the half maximal effect being obtained at 1.8 mM MgATP. In the presence of 12 mM creatine phosphate and 250 microM ADP, a decrease in MgATP concentration even to 10(-9) M never induced rigor tension. At a very low MgATP concentration (10(-6) M), the half maximal relaxing effect was obtained with 2 mM creatine phosphate, a value close to the Km of isolated MM-creatine kinase for this substrate, or with 14 microM MgADP, a value 5 times lower than the reported Km. An exogenous MgATP regenerating system (phosphoenol pyruvate + pyruvate kinase) was not able to fully relax the fibres. When MM-creatine kinase was inhibited by fluorodinitrobenzene, the dependency of rigor tension on MgATP became the same as it was without creatine phosphate. After washing out the fluorodinitrobenzene the addition of exogenous MM-creatine kinase for half an hour fully relaxed rigor tension; moreover, this effect persisted even after prolonged washout. These results show that endogenous MM-creatine kinase is able to ensure maximal efficiency of myosin ATPase by producing a localized high MgATP/MgADP ratio; they also suggest the existence of rapidly exchangeable binding sites for MM-creatine kinase in cardiac myofibrils.

Metabolite channeling: a phosphorylcreatine shuttle to mediate high energy phosphate transport between sperm mitochondrion and tail

Energy utilization by the flagellum of motile sea urchin sperm is tightly coupled to the rate of energy production by the mitochondrion. This tight coupling depends upon the transport of high energy phosphate (P) from mitochondrion to axoneme, which we propose to be mediated by a phosphorylcreatine shuttle. The shuttle employs distinct mitochondrial and axonemal creatine kinase isozymes, the latter being a novel creatine kinase of 145 kd. To examine whether P is directed to the tail by such a shuttle, we inactivated creatine kinase specifically with fluorodinitrobenzene. Creatine kinase inactivation led to an inhibition of coupled, but not uncoupled, respiration and affected the pattern of sperm motility as predicted for the disruption of an obligatory link in P transport.

Myofibrillar end of the creatine phosphate energy shuttle

Isometric contraction and relaxation of glycerinated rabbit psoas muscle fibers containing native creatine kinase (CK) and ATPase activities were studied. Energy for contraction and relaxation was provided either by ADP + creatine phosphate (CP) or ATP alone, and the effectiveness of these additions on rate and maximum force of contraction and relaxation were compared. In the presence of 250 microM ADP, physiological concentration of CP (10 mM) produced faster and stronger contraction and faster and more complete relaxation than equimolar or even higher concentrations of ATP. When contraction was initiated by addition of ADP to fibers preincubated with 10 mM CP, the apparent Km for ADP was 1.18 +/- 0.24 mM. If the fibers were preincubated with ADP and contraction initiated by addition of 10 mM CP, the apparent Km for ADP was more than an order of magnitude smaller (76.0 +/- 4 microM). The observed Km for ADP for contraction was about half the Km for CP in solution (151.5 microM). The apparent Km for CP for rate of contraction was 2.67 +/- .046 mM independent of sequence of addition of ADP. Since these experiments were done in the presence of P1,P5-diadenosine 5'-pentaphosphate, a powerful inhibitor of adenylate kinase, the role of this enzyme in the process was not significant. These observations support the idea of compartmentation of myofibrillar CK in close function with myosin ATPase as part of the phosphoryl creatine energy shuttle.

A simple analysis of the "phosphocreatine shuttle"

The diffusive mobility of solutes chemically connected by reversible reactions in cells is analyzed as a problem of facilitated diffusion. By this term we mean that the diffusive flux of any substance, X, which is in one metabolic pathway, is effectively increased when it participates in a second and equilibrium reaction with another substance Y because the total flux of X in the pathway is the sum of the fluxes of X and Y. This notion is generalized and is seen to include the familiar enhanced intracellular diffusion of oxygen by oxymyoglobin. In this framework the function of creatine kinase (CK) is seen to have two aspects: 1) phosphocreatine (PCr) via the CK reaction buffers the cellular ATP and ADP concentrations and 2) transport of high-energy phosphates is predominantly in the chemical form of PCr. This predominance of PCr is a consequence of the maintained ATP, ADP, and total creatine levels and of the apparent equilibrium constant of the reaction. Thus experimental results demonstrating the transport aspects of the CK reaction emphasize only one feature of a more general notion of facilitated diffusion by near-equilibrium metabolic reactions and do not per se establish the existence of any physical or functional compartmentation of ATP, ADP, PCr, or creatine. PCr can be a large source for increasing inorganic phosphate levels during contractile activity, possibly as a metabolic regulator. Neither the transport nor buffer aspects can be quantitatively important in cells with small distances between ATP-utilizing and ATP-generating sites, such as is the case with cardiac myofibrils and mitochondria.

Creatine kinase in regulation of heart function and metabolism. II. The effect of phosphocreatine on the rigor tension of EGTA-treated rat myocardial fibers

Bundles of rat cardiac fibers were treated with EGTA to increase the permeability of the sarcolemma to ions and small molecules. In the medium without calcium, the EGTA-treated fibers developed rigor tension dependent on the concentration of MgATP in the bathing solution: half-maximal tension was recorded at 2.5 mM MgATP and maximal tension at 0.1 mM MgATP in the medium. However, in the presence of 15 mM phosphocreatine without added creatine kinase a decrease of MgATP concentration to 0.1 mM did not result in any development of rigor tension. Phosphocreatine prevented rigor tension development in the absence of added MgATP when MgADP was added. In the presence of MgADP, phosphocreatine decreased rigor tension more rapidly and to a higher extent than added MgATP. At 5 mM MgADP, half-maximal rigor tension was observed in the presence of 2 mM phosphocreatine which is close to the Km value for phosphocreatine in the creatine-kinase reaction. These results demonstrate that the intact creatine kinase in the EGTA-treated fibers with increased sarcolemmal permeability is able to ensure rapid replenishment of MgATP in the myofibrillar compartment at the expense of phosphocreatine. The data obtained conform completely to the concept of adenine-nucleotide compartmentation in cardiac cells and of energy channelling by the phosphocreatine-creatine shuttle mechanism.

Creatine kinase in regulation of heart function and metabolism. I. Further evidence for compartmentation of adenine nucleotides in cardiac myofibrillar and sarcolemmal coupled ATPase-creatine kinase systems

In isolated and purified cardiac myofibrillar and sarcolemmal preparations, the route of movement of ADP produced in the Mg2+-ATPase reactions was studied by investigating the efficiency of competition between the endogenous creatine kinase and exogenous pyruvate kinase reactions. In the homogeneous control system composed of hexokinase and glucose as ATPase, soluble creatine kinase rapidly rephosphorylated ADP produced in the presence of 1 mM ATP, but the addition of pyruvate kinase in an increasing amount inhibited the reaction of creatine release from phosphocreatine and symmetrically increased the rate of pyruvate production from phosphoenol pyruvate. At a pyruvate-kinase/creatine-kinase activity ratio (PK/CK) of 50, all ADP was used by the pyruvate kinase. In myofibrillar and sarcolemmal preparations containing particulate creatine kinase, the creatine kinase reaction was much less efficiently suppressed by pyruvate kinase, and at PK/CK = 50 half-maximal release of creatine was still observed. The rate of immediate myofibrillar MgADP rephosphorylation in the endogenous creatine-kinase reaction was observed to be governed by the concentration of phosphocreatine in accordance with the kinetics of this enzyme. The physiological significance of these findings is discussed.