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.     

Phosphocreatine production coupled to the glycolytic reactions in the cytosol of cardiac cells

Phosphocreatine production catalyzed by a cytosolic fraction from cardiac muscle containing all glycolytic enzymes and creatine kinase in a soluble form has been studied in the presence of creatine, adenine nucleotides and different glycolytic intermediates as substrates. Glycolytic depletion of glucose, fructose 1,6-bis(phosphate) and phosphoenolpyruvate to lactate was coupled to efficient phosphocreatine production. The molar ratio of phosphocreatine to lactate produced was close to 2.0 when fructose 1,6-bis(phosphate) was used as substrate and 1.0 with phosphoenolpyruvate. In these processes the creatine kinase reaction was not the rate-limiting step: the mass action ratio of the creatine kinase reaction was very close to its equilibrium value and the maximal rate of the forward creatine kinase reaction exceeded that of glycolytic flux by about 6-fold when fructose 1,6-bis(phosphate) was used as a substrate. Therefore, the creatine kinase raction was continuously in the state of quasiequilibrium and the efficient synthesis of phosphocreatine observed is a result of constant removal of ADP by the glycolytic system at an almost unchanged level of ATP ([ATP] ? [ADP]), this leading to a continuous shift of the creatine kinase equilibrium position.When phosphocreatine was added initially at concentrations of 5–15 mM the rate of the coupled creatine kinase and glycolytic reactions was very significantly inhibited due to a sharp decrease in the steady-state concentration of ADP. Therefore, under conditions of effective phosphocreatine production in heart mitochondria, which maintain a high phosphocreatine: creatine ratio in the myoplasm in vivo, the glycolytic flux may be suppressed due to limited availability of ADP restricted by the creatine kinase system. The possible physiological role of the control of the glycolytic flux by the creatine kinase system is discussed.     

The lack of direct coupling between ATP-ADP translocase and creatine phosphokinase in isolated rabbit heart mitochondria

The formation of creatine phosphate by isolated rabbit heart mitochondria in the presence of creatine, α-ketoglutarate, ATP, and inorganic phosphate was studied. Creatine phosphate formation was inhibited by oligomycin. This was most probably due to increased concentration of ADP favoring the reverse reaction (formation of creatine and ATP from phosphocreatine and ADP). The inhibitory effect of oligomycin disappeared in the presence of phosphoenolpyruvate and pyruvate kinase. The results do not indicate any direct coupling between mitochondrial creatine phosphokinase and ATP-ADP translocase as has been suggested for rat heart mitochondria.     

Role of phosphocreatine in energy transport in skeletal muscle of bullfrog studied by 31P-NMR

To evaluate the energy-shuttle hypothesis of the phosphocreatine/creatine kinase system, diffusion rates for ATP, phosphocreatine and flux through the creatine kinase reaction were determined by 31P-NMR in resting bullfrog biceps muscle. The diffusion coefficient of phosphocreatine measured by 31P-pulsed gradient NMR was 1.4-times larger than ATP in the muscle, indicating the advantage of phosphocreatine molecules for the intracellular energy transport. The flux of the creatine kinase reaction measured by 31P-saturation transfer NMR was 3.6 mmol/kg wet wt. per s in the resting muscle. The flux is equal to the turnover rate of ATP, ADP, phosphocreatine and creatine molecules, therefore, the life-times of these substrates and the average distance traversed after the life-times by the diffusing molecules were calculated using the diffusion coefficients obtained by 31P-NMR. The mean square length of one-dimensional diffusion was 22 microns in ATP molecules and the minimum diffusion length was 1.8 microns in ADP molecules. The latter was calculated using free ADP concentration, 30 mumol/kg wet wt., obtained from the equilibrium constant of the creatine kinase reaction and the diffusion coefficient assumed to be the same of ATP in muscle. Similar diffusion lengths of ADP were calculated using the reported values for the flux of the creatine kinase reaction in heart and smooth-muscle. The diffusion lengths of all substrates involved in the creatine kinase reaction were larger than the radii of myofibrils. Therefore, in the muscles with an alternating arrangement of mitochondria and myofibrils, such as heart and certain skeletal muscles, ATP and ADP molecules can move freely between myofibrils and mitochondria without the aid of the creatine kinase reaction; thus, we conclude that the energy-shuttle hypothesis is not obligatory for energy transport between the mitochondria and the myofibrils.     

Creatine kinase of rat heart mitochondria. The demonstration of functional coupling to oxidative phosphorylation in an inner membrane-matrix preparation

To define more clearly the interactions between mitochondrial creatine kinase and the adenine nucleotide translocase, the outer membrane of rat heart mitochondria was removed by digitonin, producing an inner membrane-matrix (mitoplast) preparation. This mitoplast fracton was well-coupled and contained a high specific activity of mitochondrial creatine kinase. Outer membrane permeabilization was documented by the loss of adenylate kinase, a soluble intermembrane enzyme, and by direct antibody inhibition of mitochondrial creatine kinase activity. With this preparation, we documented four important aspects of functional coupling. Kinetic studies showed that oxidative phosphorylation decreased the value of the ternary enzyme-substrate complex dissociation constant for MgATP from 140 to 16 microM. Two approaches were used to document the adenine nucleotide translocase specificity for ADP generated by mitochondrial creatine kinase. Exogenous pyruvate kinase (20 IU/ml) could not readily phosphorylate ADP produced by creatine kinase, since added pyruvate kinase did not markedly inhibit creatine + ATP-stimulated respiration. Additionally, when ADP was produced by mitochondrial creatine kinase, the inhibition of the translocase required 2 nmol of atractyloside/mg of mitoplast protein, while only 1 nmol/mg was necessary when exogenous ADP was added. Finally, the mass action ratio of the mitochondrial creatine kinase reaction exceeded the apparent equilibrium constant when ATP was supplied to the creatine kinase reaction by oxidative phosphorylation. Overall, these results are consistent with much data from intact rat heart mitochondria, and suggest that the outer membrane plays a minor role in the compartmentation of adenine nucleotides. Furthermore, since the removal of the outer membrane does not alter the unique coupling between oxidative phosphorylation and mitochondrial creatine kinase, we suggest that this cooperation is the result of protein-protein proximity at the inner membrane surface.     

Control of heart mitochondrial oxygen consumption by creatine kinase: The importance of enzyme localization

The route of movement of ADP produced in the mitochondrial creatine kinase reaction was investigated by recording the rate of ADP-dependent oxygen consumption in the presence of phosphoenolpyruvate and pyruvate kinase. This pyruvate kinase system completely abolished activation of respiration by ADP added or by ADP produced in the hexokinase reaction in the medium, but was not able to inhibit the creatine kinase activated respiration when creatine kinase was bound to the inner mitochondrial membrane. These different responses of oxidative phosphorylation were observed at equal $\text{ATP}\text{ADP}$ ratios in the medium. The data obtained evidence direct channeling of ADP from heart mitochondrial creatine kinase to the adenine nucleotide translocase without its prompt release into the medium.     

Compartmentalized energy transfer in cardiomyocytes: use of mathematical modeling for analysis of in vivo regulation of respiration.

The mathematical model of the compartmentalized energy transfer system in cardiac myocytes presented includes mitochondrial synthesis of ATP by ATP synthase, phosphocreatine production in the coupled mitochondrial creatine kinase reaction, the myofibrillar and cytoplasmic creatine kinase reactions, ATP utilization by actomyosin ATPase during the contraction cycle, and diffusional exchange of metabolites between different compartments. The model was used to calculate the changes in metabolite profiles during the cardiac cycle, metabolite and energy fluxes in different cellular compartments at high workload (corresponding to the rate of oxygen consumption of 46 mu atoms of O.(g wet mass)-1.min-1) under varying conditions of restricted ADP diffusion across mitochondrial outer membrane and creatine kinase isoenzyme "switchoff." In the complete system, restricted diffusion of ADP across the outer mitochondrial membrane stabilizes phosphocreatine production in cardiac mitochondria and increases the role of the phosphocreatine shuttle in energy transport and respiration regulation. Selective inhibition of myoplasmic or mitochondrial creatine kinase (modeling the experiments with transgenic animals) results in "takeover" of their function by another, active creatine kinase isoenzyme. This mathematical modeling also shows that assumption of the creatine kinase equilibrium in the cell may only be a very rough approximation to the reality at increased workload. The mathematical model developed can be used as a basis for further quantitative analyses of energy fluxes in the cell and their regulation, particularly by adding modules for adenylate kinase, the glycolytic system, and other reactions of energy metabolism of the cell.     

Identification of nonmitochondrial creatine kinase enzymatic activity in isolated sea urchin mitotic apparatus

ATP-dependent calcium sequestration was previously localized in vesicles of mitotic apparatus isolated from sea urchins. We now demonstrate that the mitotic apparatus contains an ATP-regenerative system characterized as creatine kinase (EC 2.7.3.2). Mitotic apparatus isolated with vesicles intact converted ADP to ATP if phosphocreatine was present. Omission of ADP or phosphocreatine gave negligible ATP. When mitotic apparatus were washed with detergent-containing buffer to remove vesicles, their ability to produce ATP from ADP and phosphocreatine was reduced. Assays of creatine kinase activity using NADP+:glucose-6-phosphate dehydrogenase indicated that 70% of the creatine kinase activity was extractable with 0.5% Triton X-100. The insoluble residue containing the skeleton of the mitotic apparatus had the rest of the activity. Experiments with a luciferin/luciferase assay showed that Triton removed above 82% of the activity. Preparations of intact mitotic apparatus were free of cytochrome c oxidase (EC 1.9.3.1) activity and therefore free of mitochondria. About 10(8) mitotic apparatus (total volume about 1 liter) could produce 17 mmol of ATP/min when substrates were not limiting. The creatine kinase enzyme activity described herein and the previously described membrane vesicular calcium sequestration system are nonmitochondrial, integral constituents of the sea urchin mitotic apparatus.     

Glycolysis and glucose uptake in intact outer segments isolated from bovine retinal rods

Glucose transport across the plasma membrane of isolated bovine rod outer segments (ROS) was measured by uptake of 14C-labeled 3-O-methylglucose and 2-deoxyglucose and was inferred from deenergization of ROS with 2-deoxyglucose. Glucose transport was mediated by a facilitated diffusion glucose transporter that equilibrated external and internal free hexose concentrations. Glucose transport in ROS displayed two components as judged from kinetic analysis of hexose equilibration and as judged from inhibition by cytochalasin B and phloretin. Transport under exchange conditions was considerably faster as compared with net hexose uptake, similar to that observed for the erythrocyte glucose transporter. Sensitivity to cytochalasin B and affinity to 3-O-methylglucose were similar to those observed for the hepatocyte glucose transporter. The cytochalasin-insensitive component appears unique to ROS and did not reflect leakage transport as judged from a comparison with L-glucose uptake. Glucose transport feeds glycolysis localized to ROS. We suggest that a major role for glycolysis in ROS is phosphorylation of GDP to GTP via pyruvate kinase and PEP, while phosphorylation of ADP to ATP can use the creatine kinase/phosphocreatine pathway as well.     

Functional coupling of glycolysis and phosphocreatine utilization in anoxic fish muscle. An in vivo 31P NMR study

Three fish species with different strategies for anoxic survival (goldfish, tilapia, and common carp) were exposed to environmental anoxia (4, 3, and 1 h, respectively). The concentrations of high energy phosphate compounds and inorganic phosphate, besides the intracellular pH in the epaxial muscle were measured during anoxia and recovery by in vivo 31P NMR spectroscopy. The concentration of free ADP was calculated from the equilibrium constant of creatine kinase. During anoxia the patterns of phosphocreatine utilization and tissue acidification are remarkedly similar. Free ADP rises rapidly during the initial period of oxygen deficiency and reaches a plateau in goldfish and tilapia, while it keeps rising in the common carp. At elevated levels of free ADP, the creatine kinase reaction and anaerobic glycolysis are functionally coupled by H+ as a common intermediate. The coupling between both processes disappears upon reoxygenation, when mitochondrial respiration induces a rapid drop of [free ADP]. The removal of ADP shifts the creatine kinase equilibrium toward phosphocreatine synthesis despite the low pH.     

Effects of activation of protein kinase C on the agonist-induced stimulation and inhibition of cyclic AMP formation in intact human platelets.

Jakobs, Bauer & Watanabe [(1985) Eur. J. Biochem. 151, 425-430] reported that treatment of platelets with phorbol 12-myristate 13-acetate (PMA) prevented GTP- and agonist-induced inhibition of adenylate cyclase in membranes from the platelets. This was attributed to the phosphorylation of the inhibitory guanine nucleotide-binding protein (Gi) by protein kinase C. In the present study, the effects of PMA on cyclic [3H]AMP formation and protein phosphorylation were studied in intact human platelets labelled with [3H]adenine and [32P]Pi. Incubation mixtures contained indomethacin to block prostaglandin synthesis, phosphocreatine and creatine kinase to remove ADP released from the platelets, and 3-isobutyl-1-methylxanthine to inhibit cyclic AMP phosphodiesterases. Under these conditions, PMA partially inhibited the initial formation of cyclic [3H]AMP induced by prostaglandin E1 (PGE1), but later enhanced cyclic [3H]AMP accumulation by blocking the slow decrease in activation of adenylate cyclase that follows addition of PGE1. PMA had more marked and exclusively inhibitory effects on cyclic [3H]AMP formation induced by prostaglandin D2 and also inhibited the action of forskolin. Adrenaline, high thrombin concentrations and, in the absence of phosphocreatine and creatine kinase, ADP inhibited cyclic [3H]AMP formation induced by PGE1. The actions of adrenaline and thrombin were attenuated by PMA, but that of ADP was little affected, suggesting differences in the mechanisms by which these agonists inhibit adenylate cyclase. sn-1,2-Dioctanoylglycerol (diC8) had effects similar to those of PMA. The actions of increasing concentrations of PMA or diC8 on the modulation of cyclic [3H]AMP formation by PGE1 or adrenaline correlated with intracellular protein kinase C activity, as determined by 32P incorporation into the 47 kDa substrate of the enzyme. Parallel increases in phosphorylation of 20 kDa and 39-41 kDa proteins were also observed. Platelet-activating factor, [Arg8]vasopressin and low thrombin concentrations, all of which inhibit adenylate cyclase in isolated platelet membranes, did not affect cyclic [3H]AMP formation in intact platelets. However, the activation of protein kinase C by these agonists was insufficient to account for their failure to inhibit cyclic [3H]AMP formation. Moreover, high thrombin concentrations simultaneously activated protein kinase C and inhibited cyclic [3H]AMP formation. The results show that, in the intact platelet, the predominant effects of activation of protein kinase C on adenylate cyclase activity are inhibitory, suggesting actions additional to inactivation of Gi.     

Luminometric assays of ATP, phosphocreatine, and creatine for estimation of free ADP and free AMP.

We present methods to measure ATP, phosphocreatine, and total creatine (the sum of creatine and phosphocreatine) in alkaline cell extracts. Knowledge of these parameters, together with the known equilibrium constants for the creatine kinase and adenylate kinase-catalyzed reactions, allows one to estimate the levels of free ADP and free AMP inside cells. The enzymatic assays for the above-mentioned metabolites all lead up to the production of ATP, which is measured luminometrically with the ATP-dependent oxidation of luciferin catalyzed by firefly luciferase. To determine phosphocreatine, endogenous ATP is first destroyed, and phosphocreatine is then quantitatively reacted with exogenous ADP to form ATP. Total creatine is measured after quantitative conversion of creatine to phosphocreatine with a large excess of exogenous ATP, conversion of all ATP to ADP, and final reaction of phosphocreatine with ADP to form ATP. We used 5-microl samples in 0.5-ml microcentrifuge tubes and subsequent 5-microl additions of analytical reagents. We expect that the volumes can be changed easily. We tested the methods with glucagon- and insulin-secreting cells. Estimates of free ADP and AMP are expected to be useful in many different areas of research, such as cellular energy metabolism, purine nucleotide metabolism, adenine nucleotide gating of ion channels, and release of vasoactive or angiogenic factors.     

Properties and mechanism of action of creatine kinase from ox smooth muscle. Anion effects compared with pyruvate kinase

1. An improved purification procedure for the brain-type creatine kinase from ox smooth muscle is described. 2. Michaelis constants show the characteristic dependence on the concentration of the second substrate: the derived constants are compared with those for the enzyme from ox brain. 3. Inhibition by iodoacetamide gives a biphasic curve and the total extent of the reaction depends on the enzyme concentration. The rate of inhibition at pH8.6 is not affected by creatine plus MgADP or by a range of simple anions. Addition of creatine plus MgADP plus either NO(3) (-) or Cl(-) ions affords 71.5 and 44% protection respectively. ADP could be replaced by 2-deoxy-ADP but not by alphabeta-methylene ADP, XDP, IDP, GDP or CDP. Nucleotides that did not protect would not act as substrates. 4. Difference-spectra measurements support the interpretation that addition of NO(3) (-) ions to the enzyme-creatine-MgADP complex causes further conformational changes in the enzyme accompanying the formation of a stable quaternary enzyme-creatine-NO(3) (-)-MgADP complex that simulates an intermediate stage in the transphosphorylation reaction. However, the enzyme structure is partially destabilized by quaternary-complex formation. IDP apparently fails to act as a substrate because it cannot induce the necessary conformational change. This behaviour is compared with that of rabbit skeletal muscle creatine kinase. 5. With pyruvate kinase from rabbit muscle, anions activate in the absence of an activating cation and either inhibit or have no effect in its presence. 6. Both activation and inhibition were competitive with respect to the substrate, phosphoenolpyruvate, and curved double-reciprocal plots were obtained. The results may be interpreted in terms of co-operatively induced conformational changes, and this is supported by difference-spectra measurements. However, the Hill coefficient of 1 was not significantly altered. 7. Inhibition by lactate plus pyruvate is less than additive, indicating that both bind to the same site on the enzyme, whereas that by lactate plus NO(3) (-) is additive, indicating binding at separate sites. It is inferred that a quaternary enzyme-pyruvate-NO(3) (-)-MgADP complex could form, but no evidence was obtained to suggest that it possessed special properties comparable with those found with creatine kinase. The implications of these findings for the unidirectional nature of the mechanism of pyruvate kinase is discussed. 8. Lactate or alpha-hydroxybutyrate could not act instead of pyruvate to form a stable quaternary complex, although both activate the K(+)-free enzyme. Only the former inhibits the K(+)-activated enzyme. The activating cation both lowers the Michaelis constant for phosphoenolpyruvate and tightens up the specificity of its binding site.     

A theoretical model of some spatial and temporal aspects of the mitochondrion creatine kinase myofibril system in muscle

We describe a model of mitochondrial regulation in vivo which takes account of spatial diffusion of high-energy (ATP and phosphocreatine) and low-energy metabolites (ADP and creatine), their interconversion by creatine kinase (which is not assumed to be at equilibrium), and possible functional 'coupling' between the components of creatine kinase associated with the mitochondrial adenine nucleotide translocase and the myofibrillar ATPase. At high creatine kinase activity, the degree of functional coupling at either the mitochondrial or ATPase end has little effect on relationships between oxidative ATP synthesis rate and spatially-averaged metabolite concentrations. However, lowering the creatine kinase activity raises the mean steady state ADP and creatine concentrations, to a degree which depends on the degree of coupling. At high creatine kinase activity, the fraction of flow carried by ATP is small. Lowering the creatine kinase activity raises this fraction, especially when there is little functional coupling. All metabolites show small spatial gradients, more so at low cytosolic creatine kinase activity, and unless there is near-complete coupling, so does net creatine kinase flux. During workjump transitions, spatial-average responses exhibit near-exponential kinetics as expected, while concentration changes start at the ATPase end and propagate towards the mitochondrion, damped in time and space. (Mol Cell Biochem 174: 29–32, 1997)     

Relating structure to mechanism in creatine kinase

Found in all vertebrates, creatine kinase catalyzes the reversible reaction of creatine and ATP forming phosphocreatine and ADP. Phosphocreatine may be viewed as a reservoir of "high-energy phosphate" which is able to supply ATP, the primary energy source in bioenergetics, on demand. Consequently, creatine kinase plays a significant role in energy homeostasis of cells with intermittently high energy requirements. The enzyme is of clinical importance and its levels are routinely used as an indicator of myocardial and skeletal muscle disorders and for the diagnosis of acute myocardial infarction. First identified in 1928, the enzyme has undergone intensive investigation for over 75 years. There are four major isozymes, two cytosolic and two mitochondrial, which form dimers and octamers, respectively. Depending on the pH, the enzyme operates by a random or an ordered bimolecular mechanism, with the equilibrium lying towards phosphocreatine production. Evidence suggests that conversion of creatine to phosphocreatine occurs via the in-line transfer of a phosphoryl group from ATP. A recent X-ray structure of creatine kinase bound to a transition state analog complex confirmed many of the predictions based on kinetic, spectroscopic, and mutagenesis studies. This review summarizes and correlates the more significant mechanistic and structural studies on creatine kinase.     

Bioenergetic consequences of cardiac phosphocreatine depletion induced by creatine analogue feeding

To further evaluate the bioenergetic role of phosphocreatine, we assessed several parameters in normal and depleted rat hearts. Rats were fed (8 weeks) a diet containing either 1% beta-guanidinoproprionic acid or 2% beta-guanidinobutyric acid (beta-GBA), resulting in an 80% phosphocreatine depletion compared to controls. Left ventricular pressure-volume curves were obtained to determine contractile function. At any volume, the developed pressure in depleted hearts was lower than in controls. At the plateau, the rate-pressure product was between 37-45% lower: 34,000 (beta-GBA), 30,174 (beta-guanidinoproprionic acid) versus 54,400 (control). 31P NMR spectroscopy on beta-GBA-treated hearts obtained the [ATP] and [phosphocreatine], which with saturation transfer estimated the rates of creatine kinase and ATP production. In depleted hearts, the rate constant for ATP synthesis from phosphocreatine was increased 33%. However, the flux was 72% lower. ATP production from ADP and Pi were similar under normal conditions, in spite of higher rates of oxygen consumption in the depleted hearts. The addition of 50 mM creatine to control perfusate had no effect on function or high energy phosphates. In contrast, a 28% increase in function and a 52% increase in [phosphocreatine] was seen in beta-GBA hearts. There was a marked increase in free [ADP] in beta-GBA hearts, resulting in a lower estimated ATP phosphorylation potential. Overall, the results suggest that phosphocreatine may play an important function by optimizing the thermodynamics of cardiac high energy phosphate utilization.     

Affinity modification of creatine kinase and ATP-ADP translocase in heart mitochondria: determination of their molar stoichiometry

Oxidized dialdehyde analogs of ADP or ATP (oADP and oATP) were shown to inhibit irreversibly adenine nucleotide translocator (T) and creatine kinase (CK) in heart mitochondria. Inactivation of T and CK was parallel with carboxyatractyloside - sensitive and (ADP + phosphocreatine) - sensitive incorporation of o[3H]ADP into mitochondria, respectively. o[3H]ADP incorporation sensitive to CAT or ADP+phosphocreatine was used to determine T and CK contents in mitochondria. T content in cardiac mitochondria from rat, rabbit, dog, and chicken was calculated to be 2.6 - 2.9 moles/mole cyt.aa3. The same value of T/cyt.aa3 ratio was found in liver mitochondria with lower cytochrome aa3 content. In all types of cardiac mitochondria CK content was found to be 2.4 - 2.6 moles/mole cyt.aa3. The data show that T and CK are present in molar ratio 1:1 in all types of cardiac mitochondria.     

31P-NMR spectrum of phosphocreatine: Deuterium-induced splitting of the signal

It has been found in experiments with high resolution ³¹P-NMR spectroscopy (200 MHz) that the phosphocreatine peak is splitted into two different peaks in the mixtures of H₂O and D₂O and is single but with different chemical shifts in pure H₂O and D₂O. This phenomenon is explained by substitution of protons of guanidino group in phosphocreatine by deuterium. The effect of splitting disappeared at extreme pH values (>8.5 or <4.0) and at temperatures higher than 45°C due to accelerated proton-deuterium exchange. Creatine kinase added to phosphocreatine solution also lowered its temperature of peaks' collapse by 5°–10°C. A saturation (spin) transfer method was used to show that the phosphoryl group transfer to ADP in creatine kinase active center is slower with deuterium-substituted phosphocreatine than with H-phosphocreatine. The data are taken to show the importance of the proton transfer step in the creatine kinase reaction mechanism and acceleration of phosphocreatine proton-deuterium exchange by creatine kinase.     

Synthesis of phosphocreatine in heart mitochondria of rats with hyperthyroidism

The mechanisms of the phosphocreatine/creatine ratio decrease in female Wistar rats with hyperthyroidism were studied. L-Thyroxin was injected to animals in doses of 50 and 100 micrograms/100 g of body weight, daily for 1 and 2 weeks. Oxidative phosphorylation and the rate of phosphocreatine synthesis were studied in isolated rat heart mitochondria. It was found that hyperthyroidism caused an increase in the ADP-activated mitochondrial respiration, whereas the coupling between electron transport and ADP phosphorylated remained at a constant level. Besides oxidative phosphorylation, activation, hyperthyroidism increased the rate of phosphocreatine synthesis at high values of the phosphocreatine/oxygen ratio. Thus, hyperthyroidism is unaccompanied by and significant changes in the coupling of mitochondrial creatine kinase with oxidative phosphorylation.