Further observations on phosphagen

CHEMICAL CHANGES IN THE ADDUCTOR MUSCLE OF THE CHELIPED OF THE CRAYFISH IN RELATION TO THE DOUBLE MOTOR INNERVATION

An investigation has been made of the phosphate and lactic acid changes in the adductor muscle of the cheliped of the crayfish Cambarus clarkii upon stimulation of the isolated axons for the fast and slow contractions at determined frequencies. The data obtained point to the following conclusions: 1. When the mechanical effects of the two types of contraction are the same, the chemical changes are of the same order. If the mechanical effects are different, the chemical changes likewise are not equivalent. This is especially to be seen in the case of stimulation at 50 shocks per second: a slowly rising, long continued, strong slow contraction takes place with no apparent change in the phosphate content; a quickly rising fast contraction occurs with a large increase in the phosphate. 2. Since equivalent chemical changes accompany equivalent mechanical action, the two types of contraction do not differ in the essential mechanism of the chemical changes involved, and only one type of contractile substance is present. 3. Even when a contraction has taken place to the maximum extent obtainable, only enough phosphate is found to correspond to one-fifth to one-third of the available phosphagen.

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.

Functional aspects of the X-ray structure of mitochondrial creatine kinase: a molecular physiology approach

Mitochondrial creatine kinase (Mi-CK) is a central enzyme in energy metabolism of tissues with high and fluctuating energy requirements. In this review, recent progress in the functional and structural characterization of Mi-CK is summarized with special emphasis on the solved X-ray structure of chicken Mib-CK octamer (Fritz-Wolf et al., Nature 381, 341-345, 1996). The new results are discussed in a historical context and related to the characteristics of CK isoforms as known from a large number of biophysical and biochemical studies. Finally, two hypothetical functional aspects of the Mi-CK structure are proposed: (i) putative membrane binding motifs at the top and bottom faces of the octamer and (ii) a possible functional role of the central 20 A channel.

Myothermic apparatus

The investigation to be described in subsequent papers represent an attempt to clear up, with the greatest accuracy possible, a number of outstanding or controversial points in connection with the energy exchanges of muscle. During the course of them a new and striking phenomenon has been encountered, in respect of the resting heat-production of muscles kept under strictly anaerobic conditions. It has been necessary, moreover, for various purposes, to follow the heat-production of stimulated or recovering muscles for long periods, sometimes for an hour or more. The apparatus available proved inadequate for these new purposes, and had to be designed and constructed afresh. The present paper is a description of the methods finally adopted; the results obtained are given separately. In almost every respect the apparatus now employed will yield more reliable results, and is simpler to use, than any previously described, at any rate by the present author. The essential condition which it fulfils is that it will read, with relative accuracy, not only the heat suddenly produced by a single stimulus, but that liberated over long intervals at rest, or in recovery, or by prolonged discontinuous stimulation.

Anaerobic survival in muscle

During the anaerobic survival of muscle it is well known that lactic acid is formed, and it has recently been found that a compound of phosphate and creatine is broken down (Eggleton and Eggleton (1)). Both these reactions can be reversed in tire presence of oxygen. No other processes are known as yet to occur. It seemed possible that anaerobic survival might involve not only the formation of simple chemical substances capable of diffusing from, or of being isolated from, the tissue, but also an alteration of some kind in the machinery of the muscle cell itself, which also in the presence of oxygen might be reversed. From a thin enough muscle suspended in Ringer's solution we can remove, by prolonged diffusion, the major portion of the lactic acid. If lactic acid production were the only accompaniment of anaerobic survival, the continual removal by diffusion of this substance would allow the muscle to remain in its initial resting state until such time as the whole of its carbohydrate store was exhausted. Taking account of the phosphagen break-down the muscle might be expected to become slower in its time-relations, since speed of contraction seems to be associated with phosphagen content and breakdown (Eggleton and Eggleton (1), Nachmansohn (2), Meyerhof (3)). The phosphate liberated could be prevented from escaping by increasing the phosphate concentration in the Ringer's solution (Stella (4)), though this would probably not prevent the phosphagen breakdown. Creatine is not known with certainty to escape.

The absolute value of the isometric heat coefficient TI/H in a muscle twitch, and the effect of stimulation and fatigue

It is not technically possible to determine directly the lactic acid set free in a sing1e muscle twitch. It is necessary to calculate it from the initial heat production, or from the tension developed. The anaerobic liberation of 1 gramme of lactic acid in musc1e is accompanied, according to Meyerhof, by the production of 385 calories of heat (1). This 1eads to the equation:- 1 gramme-cm.(heat) ≡ 6·14 × 10 -8 gramme lactic acid. (I) The isometric coefficient of lactic acid, defined for a twitch or a series of twitches by the equation* K m =(grammes tension developed) (cms. muscle length)/(grammes lactic acid produced), has been the subject of much investigations by meyerhof and his colleagues (2, 3, 4, 5). Matsuoka, for the frog's sartorius muscle in Ringer's solutions, found a mean value of 1·05 × 10 8 (variation 0·69 to 1·36). Meyerhof and Lohmann, for frog's gastrocnemius, gave 1·40 × 10 8 as a mean, while Meyerhof and Suchulz gave 1·43 × 10 8 (variation 1·12 to 1·66). In the gastrocnemius, however, the fibres are not straight, and do not run parallel to the muscle length; consequently it is necessary to mutiply (see Mashino(6), A. V. Hill(7)) the value so found by a factor of roughly 0·63 to allow for the skew disposition of the fibres. This gives, when corrected, 0·9 × 10 8 for the gastrocnemius, so that taking account of the value 1·05 × 10 8 found by Matsuoka for the sartorius, the round figure 1 × 10 8 may be accepted. This leads to the equation:- 1 gramme-cm.(tension-length) ≡ 10 -8 gramme lactic acid.

The anaerobic delayed heat-production after a tetanus

In a previous paper of this series it was shown by one of us that, in the case of a regular succession of separate twitches, there is no considerable anaerobic delayed heat-production: the only important after-effect of such anaerobic stimulation is a permanent increase in the resting beat-rate. It was pointed out there that this increment, produced by activity, in the basal beat-rate, cannot be regarded as part of the contraction-process itself, though it may easily be misinterpreted; unless the galvanometer-sere and the temperature of the thermopile be very steady, this permanent increase may be mistaken for a long-continued delayed heat associated with contraction and ending in 10 or 15 minutes. The diagram of fig. 1 illustrates this point, At time zero the muscle is stimulated by a short tetanus and the galvanometer deflects, returning to a constant position—but not to its original one—in about 3 minutes. The displacement from the initial position is a measure of the increment in resting heat-rate. This increment must be supposed to occur at, or immediately after, the moment of contraction. There is no obvious reason why it should occur at any other moment. If so, the baseline from which the area of the deflection-time curve must be calculated is the continuation backwards of the line representing the final level attained by the galvanometer. Now let us imagine that owing to galvanometer instability, or to gradual temperature change in the thermopile, there is a slow, small and not quite regular creep of the spot of light on the scale. The only way to proceed is to allow a sufficient time to elapse after stimulating and to join the initial to the final position, so obtaining a base-line ( e. g ., B in the diagram) from which to measure the area of the deflection-time curve. It is obvious that a greater area will thus lie found than if the correct base-line A bad been adopted. His case illustrated in the diagram is exaggerated. It will made clear, however, how an error may occur unless extreme stability of galvanometer and thermostat be available. We have found, employing the present apparatus, in all cases, whether of short tetanic stimuli or of a series of single shocks, that with the thermopiles used the galvanometer becomes quite steady again in 3 or 4 minutes: there is no long-continued delayed anaerobic heat , such as was described by ourselves (1) (2) and by Furusawa and Hartree (3). The genuine anaerobic delayed heat is confined to the first 2 or 3 minutes after stimulation.

Intracellular compartmentation, structure and function of creatine kinase isoenzymes in tissues with high and fluctuating energy demands: the 'phosphocreatine circuit' for cellular energy homeostasis

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Enzymatic erythrocyte creatine determinations as an index for cell age

Creatine concentration in red blood cells was determined after ammoniumsulfate precipitation on a clear hemoglobin-free filtrate with a new enzymatic assay making use of bacterial creatinase. The method described is more specific than Griffiths' method and can easily be mechanised and adapted for use in a routine laboratory using classical automated equipment. By contrast with Griffiths' method no significant interferences of amino acids and creatine-like molecules were found. Reference values for this method were 0.379 +/- 0.076 mmol/l. In patients with high turnover of erythrocytes, e.g. haemodialysis patients (0.529 +/- 0.122 mmol/l), and renal insufficiency patients (0.565 +/- 0.145 mmol/l), significantly increased creatine concentration in erythrocytes were observed. Low erythrocyte creatine concentrations were found in chronic ambulatory dialysis patients (0.311 +/- 0.042 mmol/l).

Mechanical relaxation rate and metabolism studied in fatiguing muscle by phosphorus nuclear magnetic resonance

1. We have used phosphorus nuclear magnetic resonance (31P NMR) to study muscular fatigue in anaerobic amphibian muscle. In this paper the biochemical and energetic changes that result from a series of tetani are related to the decrease in rate constant (1/tau) for the final, exponential, phase of relaxation. 2. Using 31P NMR we have measured the concentrations of phosphocreatine (PCr), inorganic phosphate (Pi) and ATP as well as the internal pH. From our measurements we have calculated [creatine], [free ADP], the free-energy change (more precisely, the affinity A = -dG/d xi) for ATP hydrolysis and the rates of lactic acid production and of ATP hydrolysis. 3. We have found that 1/tau, the rate constant of relaxation, is correlated with each of the following, independently of the pattern of stimulation: isometric force production, all of the measured or calculated metabolite levels, pH and dG/d xi. 4. There is a clear dependence upon the pattern of stimulation of the relation between 1/tau and each of the following: total duration of the experiment, number of contractions, rate of lactic acid production and rate of ATP hydrolysis. 5. The rate of relaxation is linearly related to [PCr], [creatine], [Pi] and dG/d xi. It is nonlinearly related to isometric force, [ATP], [H+] and rate of ATP hydrolysis. 6. We conclude that the change in 1/tau, like that of isometric force, depends upon metabolic factors, and not upon any independent changes in the activation or deactivation of contraction. We suggest that 1/tau may depend upon the free-energy change for ATP hydrolysis which in turn may be related to the rate of Ca2+ uptake into the sarcoplasmic reticulum.

Distribution of creatine, guanidinoacetate and the enzymes for their biosynthesis in the animal kingdom. Implications for phylogeny

1. The distribution of creatine and the creatine-synthesizing enzymes in the animal kingdom has been investigated. Creatine was found in tissues of all vertebrates examined, and in various invertebrates from phyla Annelida, Echinodermata, Hemichordata and Chordata, subphylum Cephalochordata. The activities of the creatine-synthesizing enzymes, arginine-glycine transamidinase and guanidinoacetate methylpherase, were not detected in the hagfish or in any of the invertebrates, including those in which creatine was found, with the exception that transamidinase activities were detected in the amphioxus and salt water clam; however, these activities are considered to be artifacts for reasons mentioned in the text. Additional evidence that the hagfish and various creatine-containing invertebrates could not synthesize creatine was the observation that these animals did not convert one or the other of the likely precursors of creatine (arginine and glycine) into creatine, in vivo. Further, the inability of these animals to synthesize creatine is correlated with the observations that all animals tested were able to abstract creatine from their aqueous environment. 2. The activities of the creatine-synthesizing enzymes were detected in the sea lamprey and in all but a few of the other vertebrates examined. Neither activity could be detected in the sharks and rays (cartilaginous fish), buffalo fish (bony fish) or the snapping turtle. Transamidinase or guanidinoacetate methylpherase activity could not be found in the salamander or garter snake, respectively. 3. The results obtained with the lamprey are in direct contrast with those obtained with the hagfish (both subphylum Agnatha, class Cyclostomata). The lamprey had the ability to synthesize creatine and did not abstract creatine from lake water. The hagfish did not have any apparent ability to synthesize creatine and did abstract creatine from sea water. The present report thus supports the theory that the myxinoid (hagfish) and petromyzoid (lamprey) agnathans are only distantly related. 4. The lack of creatine-synthesizing enzyme activities in the cartilaginous fishes may have phylogenetic significance, but may also be explained by the availability of creatine in the diet of these animals. The lack of one or both enzyme activities in vertebrates other than the hagfish and the cartilaginous fish is suggested to be the result of creatine in the diet.