SWITCHING DYNAMICS AND THE TRANSIENT MEMORY STORAGE IN A MODEL ENZYMENETWORK INVOLVING CA2+ CALMODULIN-DEPENDENT PROTEIN-KINASE-II IN SYNAPSES/

The signal processing through a chain of phosphorylation-dephosphoryla tions mediated by a pair of enzymes, Ca2+/calmodulin-dependent protein kinase II and the associated phosphatase, is formulated as a non-auto nomous dynamical system in the framework of non-autocatalytic, intraho loenzyme reaction dynamics. A classification of switching characterist ics of the system is made in the parameter space comprising the three controllable system parameters: an input-pulse intensity and initial c oncentrations of the two associated enzymes. It is found that a region of parameter space exists termed the transition zone, that exhibits a quasi-switching behaviour characterized by a signal storage time bein g prolonged by more than several orders of magnitude (10(4) times in c ertain cases) for the increase of two orders of magnitude in the input signal intensity. The effect of alterations of certain rate constants on the quasi-switching property is explored. It is numerically demons trated that the Ca2++/calmodulin-dependent kinase II-related phosphata se is the most important key enzyme for regulating the signal storage time.