The turnover of phosphorus compounds in crab muscle fibres.

Abstract

SUMMARY1. The exchange of 32p injected into single crab muscle fibres as either orthophosphate or ATP has been studied. The results have been analysed in terms of a simple kinetic model.2. The exchange of 32p between ATP and arginine phosphate is considerably faster than that between ATP and orthophosphate during rest and during contraction in caffeine.3. The rate constants obtained at rest after the injection of either orthophosphate or ATP labelled with 32p were of the same order. They were also of the same order as those which have been obtained previously for squid axons.4. The exchange during caffeine contraction of 32p injected as orthophosphate gave rate constants which were consistent with an increased rate of splitting of ATP and with the rate constants needed to account for the observed net formation of orthophosphate. The results obtained after the injection of 32P-labelled ATP during caffeine contraction were less clear cut.

Phosphate fluxes in single muscle fibres of the spider crab, Maia squinado.

“…2, 4, 5 and 6. Similar results for the rate of equilibrium between injected orthophosphate and organic phosphates have also been obtained by Caldwell & Walster (1975).…”

“…The method used was similar to that of Caldwell & Walster (1975). In experiments 32p_ labelled orthophosphate of high specific radioactivity was first injected into a single Maia muscle fibre.…”

“…The distilled water was injected into the fibre and then fairly quickly sucked back into the injector so that a very small sample of the contents of the sarcoplasmic fluid was obtained. In the present work the sample was quickly transferred into a small quantity of cold aqueous trichloroacetic acid and then chromatographed at 0°C on paper in one dimension in the ethanol: trichloroacetic acid solvent used by Caldwell & Walster (1975). The counts in the ATP, arginine phosphate and orthophosphate fractions were determined and expressed as a % of the total counts to give relative activities.…”

A possible mechanism of glycolytic impairment after adenosine triphosphate deplection in the perfused rat heart.

“…To overcome these difficulties in circumstances where some metabolic concentrations are known with confidence, other concentrations can be calculated by assuming equilibrium of the adenylate kinase and creatine kinase reactions (Hiltunen & Hassinen, 1976;Williamson et al 1976). However, the equilibrium assumption may not always be valid for the adenylate kinase reaction, as indicated by evidence of 32p turnover in crab muscle ATP (Caldwell & Walster, 1975); moreover, in severe ATP depletion, no individual adenine nucleotide concentrations are established to provide a starting point for this approach. In the absence of precise guidelines, the kinetic calculations (see Results) were carried out using adenine nucleotide concentrations of 100, 80 and 50 % of the measured values; in each case, a severe hexokinase block was predicted, suggesting that the intracellular adenine nucleotide concentrations, though not precisely known, may be in a range which causes glycolytic impairment at the hexokinase step.…”

An investigation of myoplasmic magnesium adenosine triphosphate in barnacle muscle fibres with the firefly method.

“…In the experiments described in this paper, the firefly luminescence system has been injected into single muscle fibres from the barnacle Balanus nubilus to see if it is possible to obtain information about the state of distribution of the internal fibre ATP. This is a matter of some interest since Caldwell & Walster (1975) obtained indications that injected 32P-labelled ATP was not equivalent to the fibre ATP in single muscle fibres from the crab, Maia squinado. Preliminary accounts of some of this work have already appeared (Bittar & Keh, 1978;Bittar & Chiang, 1978).…”