An investigation into the turnover rates of organophosphates. 2. The rate of incorporation of 32P into adenosine triphosphate and phosphocreatine in skeletal muscle

Abstract

The effect of perfusion and of cooling of skeletal muscle on specific radioactivity of the 3 P atoms of adenosine triphosphate, phosphocreatine P and inorganic P was investigated. The procedures resulted in marked changes in specific radioactivities of these compounds when compared with specific radioactivities of the same compounds isolated from muscle dropped immediately into liquid O2- The most important changes which occurred were a breakdown of weakly labelled organophosphorus compounds with a dilution of specific radioactivities of the intracellular inorganic pool, a fall in specific radioactivity of the terminal P atom of adenosine triphosphate, a rise in specific radioactivity of the middle P atom and a fall in specific radioactivity of phosphocreatine P. The relative turnover rates of the 3 P atoms of adenosine triphosphate and phosphocreatine P were measured. The terminal P atom of adenosine triphosphate was replaced 6-8 times more often than the middle P atom, and this latter is replaced about 16 times more often than the P atom attached to the ribose moiety of the molecule. Phosphocreatine P is replaced at about the same speed as is the terminal P atom of adenosine triphosphate, although some doubt exists as to the validity of the methods used for this detn. The need to ensure complete cessation of enzyme action at the end of expts. which use isotopes has been stressed.