Arginine kinase and the rate of turnover of ATP in muscles
The muscles are able to work with high frequency for a long time, possess a high capacity for aerobic ATP synthesis and, consequently, a high density of mitochondria. In flight muscles of bees, the density of mitochondria in the cell volume reaches 43% (Suarez, 1996), and the myofibrils occupy up to 54% (Suarez et al . 2000). Synchronous muscle, working with a high frequency, require a large rate of change of concentration of ions of Ca 2+ by the sarcoplasmic reticulum (SR). Many insects, especially Hymenoptera and Diptera, have asynchronous type of the muscles, characterized by very weak development of the SR, so the high rate is associated with a density of mitochondria, but not with the density SR (Josephson et al . 2000) and for ATP resynthesis after hydrolysis cell Atrasou responds to oxidative phosphorylation in mitochondria.
Myofibrils, mitochondria and SR in muscle cells are so densely Packed that it is appropriate to ask a rhetorical question: “where is cytosol?” (Suarez, 2003).
Since the turnover rate of ATP depends on the distance between the mitochondrial ATP sentati and active Atrasou of actomyosin, here we are faced with one exception to the generalization that the gradient of intracellular metabolites are not essential for metabolism. For the process of muscular work requires a high speed diffusion current ADP of myofibrils, where the actomyosin of Atrasa catalyzes the hydrolysis of ATP to ADP and phosphate in the mitochondria where ATP resynthesised. Concentration of free ADP in the cytoplasm of muscle cells so low due to the very high rate of turnover of ATP (Jacobus, 1985) and consequently the intracellular gradient ADP insufficient to ensure an adequate flow from the myofibrils to the mitochondria.
It is found that in skeletal and cardiac muscles of vertebrates approximately half of the enzyme creatine kinase (CK) is in the sarcoplasm, and the second half in particular the isoforms is bordered by mitochondria and myofibrils.
The issue of limitation of oxidative phosphorylation in mitochondria the rate of diffusion of the ADP is accommodated by diffusion of creatine (Cr) from the myofibrils to the mitochondria, where under the influence of IC phosphorylated creatine, getting a phosphate group from ATP and diffuses back into the myofibrils in the form of creatine phosphate (CrP). In the myofibrils ATP is hydrolyzed by Atrasou of actomyosin ADP and received refosfauriliruetsa using CrP in a reaction catalyzed by myofibrillar CK. The essence of this cycle, called Shuttle (Meyer et al . 1984; Dzeja, Terzic, 2003), is that the transport function of creatine and CrP consist of a simple sequence of equilibrium States creatine kinase reactions.
Consider these two processes separately. Write the hydrolysis reaction and repositoryservice in myofibrils:
ADP 3- + CrP + H + → ATP 4- + Cr
A generalized reaction 1:
The reaction of formation of ATP and CrP in the mitochondria:
Cr + ATP 4- → CrP + ADP 3- + H +
A generalized reaction 2:
In the first case, creatine and ion-phosphate are the products of the reactions in the second – consumable components. Both reactions are under the control of creatine kinase. This suggests that in the Shuttle mechanism involved creatine and ion-phosphate on one side and creatine phosphate with the other, and ATP and ADP are not a part of this. All invertebrates and insects in particular, instead of creatine phosphate in providing working muscles with energy participates more ancient connection – arginine phosphate. The vertebrate creatine is a derivative of arginine.
In this respect it is important to analyse the conditions of collection and storage of live material prior to analysis. According to Read et al . (1977), insects (bumblebees, wasps, bees) were caught during the forage was used on the same day or the next and was maintained at 5° C (insect flight muscles were removed after cooling the insect at 5° C ), and by Newsholme et al . (1978) – the material was used immediately after catching, without specifying the temperature. Recalculation of the activity oxoglutarate dehydrogenase in the turnover rate of ATP are shown in table 7. In the work of Wegener et al . (1986) present data on the activity of adenylate kinase and the rate of turnover of ATP in the bumblebee Bombus agrorum (120 and 1017 µmol /min per g muscle, respectively) and bees Apis mellifera (954 49 and µmol /min per g muscle, respectively) with reference to Newsholme et al . (1978), where, however, the data for bees are absent. Adenylate kinase (makinana) reaction in the myofibrils shall defosfaurilirovnie the Asia-Pacific region with an excess of ADP, in conjunction with arginine kinase increases the turnover of ATP in muscles: 2 ADP → ATP + AMP . However, even the combined effect of arginine kinase and adenylate kinase are significantly inferior to the rate of turnover of ATP in the mitochondria. Since the temperature at which contains living material, can significantly affect the rate of glycolysis and, consequently, on the rate of turnover of ATP to working muscles, it is useful to compare the rate of turnover of ATP with the conditions of the material to the conduct of biochemical tests (table 7).
Table 7. The influence of the external temperature and the functional load on the rate of ATP turnover in bees and Bumble bees.