Epinephrine signaling, like that of insulin, is a multi-step pathway with several amplification steps. Identify the steps below which are interactions at an allosteric site or an enzyme active site. Abbreviations: Epi (epinephrine), 2AR ( 2 adrenergic receptor), R2C2 (subunit composition of protein kinase A where R is the regulatory subunit and C is the catalytic subunit), PDE (cyclic AMP phosphodiesterase), PPase (phosphoprotein phosphatase)..