複選題32. Which of the following descriptions regarding G protein signaling are correct? (A) G protein complex is composed of the variable Ga and the invariable Gẞy subunits. (B) Ga could lead to the activation of adenylate cyclase, which hydrolyzes phospholipids to produce two important second messengers, diacyl glycerol (DG) and inositol 1,4,5-triphosphate (IP3) (C) Protein kinase A (PKA) is composed of two catalytic subunits and two regulatory subunits, and cyclic AMP binds the latter to release and activate the catalytic subunits (D) G protein-coupled receptors (GPCR) signaling can be terminated by endocytosis-mediated removal of GPCR or clearance of second messengers by phosphodiesterases or intracellular calcium buffer system (E) DG exerts its effects by triggering increase of intracellular calcium level, whereas IP3 directly activates protein kinase C