Answer
The two molecules are ADP and creatine phosphate (CP).
Catalysis is accomplishesd by the enzymes myokinase and creatine kinase.
Myokinase adenylate kinase) catalyses the transfer of a Pi from one ADP to another:
ADP+ADP<>ATP+AMP
( magnesium is necessary for this reaction)
Work Step by Step
Creatine kinase (phosphocreatine kinase) catlyzes the reaction that obtains a Pi from creatine phosphate (PCr) and donates it to an ADP:
ADP+PCr<>ATP+Cr
