31P-NMR studies of phosphate metabolites in intact red and white swimming muscles of cod (Gadus morhua L.).

31P-NMR was used to characterise intracellular phosphate pools and their post mortem changes at 7 degrees C in intact red and white cod muscles under anaerobic conditions. A total phosphate content of 55 and 60 mM was observed in red and white muscle, respectively. The concentration of P-creatine was 14 mM in the white and 9 mM in the red muscle, while that of inorganic phosphate, Pi (30 mM), ATP (9 mM), and sugar phosphate (5 mM) were similar in both muscles. During the first 90 min after death, the decrease in P-creatine showed a first order breakdown with a concomitant stoichiometric increase in Pi content, whereas the ATP and sugar phosphate remained the same. The intracellular pH decreased from 7.4 to 7.3 in this period. The steady-state rate constant of myosin ATPase was 0.0054 and 0.0022/min for red and white muscles, respectively. Individuals kept under diminished oxygen tension prior to being killed, showed a reduced P-creatine level in both muscles.