Final answer:
The statement is false; both G-Protein-Mediated Signal Transduction involving PKA and PKC activation depend on different factors and processes. PKA becomes active upon cAMP binding, while PKC activation is aided by the presence of calcium and DAG, not inhibited by PKA phosphorylation.
Step-by-step explanation:
The statement that G-Protein Kinase (GPK) can be active when bound to calcium, but not when phosphorylated by Protein Kinase A (PKA) is False. G-Protein-Mediated Signal Transduction involves the interaction between effectors such as hormones and their receptors, leading to the activation of various intracellular pathways. One such pathway involves the activation of PKA, where a conformational change upon cAMP binding results in the dissociation of its subunits, with two becoming catalytically active. These active subunits may phosphorylate other enzymes, such as phosphorylase kinase, resulting in varied cellular responses.
Furthermore, Protein Kinase C (PKC) is activated in a different manner, involving the generation of diacylglycerol (DAG) and inositol triphosphate (IP3) by an effector-activated phospholipase C. DAG and IP3 then work together to release calcium from the endoplasmic reticulum and activate PKC. PKC, when active, can phosphorylate various substrates, including inhibitory proteins like IK-B which, upon phosphorylation, releases NF-kB to initiate RNA transcription. Therefore, PKC can be active in the presence of calcium, and PKA phosphorylation triggers a cascade that could lead to the activation of various enzymes, not deactivation.