Phosphagen, muscle

Figure 31-3. Arginine, ornithine, and proline metabolism. Reactions with solid arrows all occur in mammalian tissues. Putrescine and spermine synthesis occurs in both mammals and bacteria. Arginine phosphate of invertebrate muscle functions as a phosphagen analogous to creatine phosphate of mammalian muscle (see Figure 31-6).

Storey, K.B. Purification and characterization of arginine kinase from the mantle muscle of the squid, Symplectoteuthis oualaniensis. Role of the phosphagen/phosphagen kinase system in a highly aerobic muscle. Arch. Biochem. Biophys., 179, 518-526 (1977)... 

ATP provides the immediate source of energy for muscles but its concentration is only -5 mM. As discussed in Chapter 6, Section D, phosphagens, such as creatine phosphate, are also present and may... 

Muscle and other tissues from both vertebrates and invertebrates usually contain a reserve of high-energy phosphate in the form of phosphagens. The phosphagens are all guanidines and they react reversibly with ATP ... 

The simplest mechanism for generating ATP is phosphagen mobilization. In vertebrate tissues such as muscle containing creatine phosphate (PCr) this mobilization is catalyzed by creatine phosphokinase (CPK), a process which requires no 02 and can be written as follows ... 

Other phosphagens (such as arginine phosphate, lombrocine phosphate, tauromyocine phosphate) are found in many invertebrate muscles. 

Karlsson, J, (1971) Lactate and phosphagen concentrations in working muscle of man. Acta Physiol. Scand. Suppl. 358 1-72. Astrand, P.-O. and Rodahl, K. (1977) Textbook of Work Physiology, pp. 182-4, McGraw-Hill, Inc., New York, NY. 

Energy rich phosphagens In dynamic and static work. In Muscle Metabolism During Exercise (Pernow, B. and Saltln, B., eds.), pp. 341-55, Advances In Experimental Medicine and Biology, Vol. 11, Plenum Press, New York, NY. 

Creatine functions as a phosphagen in muscle. Neither the small amount of ATP in muscle nor the speed with which metabolic activity can be increased, and hence ADP be rephosphorylated, matches the demand for ATP for rapid or sustained muscle contraction. Muscle contains a relatively large amount... 

Meyerhof O and Lohmann K, The natural guanidinophosphoric acids (phosphagens) in striated muscle. II. Physico-chemical properties of the guanidinophosphoric acids, Biochem. Z., 196, 49-72 (1928). Cited in Perrin Bases 3410 ref. M41. CA 23 7362. 

During periods of rest when ATP is abundant, creatine is phos-phorylated by creatine kinase to form phosphocreatine. This reaction is especially important in muscles. When a sudden explosive burst of muscle activity occurs, phosphocreatine phosphorylates adenosine diphosphate (ADP) to generate the ATP needed for muscle contraction (Fig. 10.4). For this reason, phosphocreatine is known as a phosphagen . 

He worked on the sources of energy for muscular contraction, a continuation of his first interest in muscle creatine. Phosphagen had been recently discovered. Einar Lundsgaard had just shown that muscle poisoned with iodoacetic acid was able to perform a certain amount of work without liberation of lactic acid. Using muscles with low carbohydrate content, Ochoa was able to demonstrate the muscle s ability to perform work using sources of energy different from those then known. It was an important piece of work on a topic of great interest at the time. 

Upon returning to Madrid from Germany in 1931, Ochoa married Carmen Cobian. He resumed his work at the Physiology Laboratory as an Associate Professor. He devoted most of his time to work on the chemistry and energetics of muscle contraction. He found proof for the existence of a fraction of combined creatine which differed from phosphagen. He also continued studies on chemical changes associated with adrenal insufficiency. 

It was noted above that the small amount of ATP in the body turns over rapidly, and ADP is rapidly rephosphorylated to ATP However, neither the small amount of ATP in muscle nor the speed with which metabolic activity can be increased, and hence ADP can be rephosphorylated, matches the demand for ATP for rapid or sustained muscle contraction. Muscle contains about four times more creatine phosphate than ATP as shown in Figure 3.11, this acts as a reservoir or buffer to maintain a supply of ATP for muscle contraction until metabolic activity increases. Creatine phosphate is sometimes called a phosphagen because it can be used to rephosphorylate ADP to ADP. 

Because of its role as a phosphagen in muscle, creatine supplements are often used as a so-called ergogenic aid, to enhance athletic performance and muscle work output. In subjects who have an initially low concentration of creatine in muscle, supplements of 2-5 g of creatine per day do increase muscle creatine however, in people whose muscle creatine is within the normal range, additional creatine has little or no effect. 

Creatine phosphagen is only found in the muscles of vertebrates, its function among the invertebrates being fulfilled by ajginine phosphagen (p. 313). 

In the resting muscle, at least 95 per cent, of the creatine is in the bound form of creatine phosphagen, and is maintained at this level by the plasma creatine, which is in equilibrium with the free creatine of the muscle. Creatine is continually being synthesised in accordance with the phosphagen requirements of the muscular and possibly other systems, the surplus being excreted as creatinine. 

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