Final answer:
Calmodulin is the Ca2+-binding protein that activates many enzymes, including myosin light-chain kinase, which is essential for muscle contraction in both striated and smooth muscles.
Step-by-step explanation:
A Ca2+-binding protein that activates many enzymes, including myosin light-chain kinase, is calmodulin (option C). Calmodulin plays a critical role in the calcium signaling pathway. When calcium ions bind to calmodulin, it undergoes a conformational change that allows it to activate various enzymes and proteins, including myosin light-chain kinase which plays a crucial role in muscle contraction. This is especially important in smooth muscle, where calcium binding to calmodulin triggers an enzyme cascade that leads to the phosphorylation of myosin light chains and thus muscle contraction. The interaction between calcium, calmodulin, and myosin light-chain kinase is a key component in the regulation of muscle contraction both in striated muscles, like skeletal and cardiac muscles, and in non-striated muscles, such as smooth muscles.