Calmodulin-like Ca2+-Binding Proteins of Smooth Muscle
Ca2+ ions serve as intracellular messengers mediating the effects of a variety of extracellular signals (hormones, neurotransmitters, growth factors, etc.) in eliciting appropriate physio logical responses (Carafoli and Penniston, 1985). For example, the neurotransmitter acetylcholine causes an elevation of cytosolic [Ca2+ ] in smooth muscle leading to contraction. The effects of Ca2+ ions are mediated by a number of Ca2+ -binding proteins (Kretsinger, 1980). Calmodulin is one such Ca2+ -binding protein which responds to physiological [Ca2+ ] transients by binding Ca2+ and undergoing a conformational change (Klee, 1977) which includes exposure of a hydrophobic site(s) (LaPorteet al., 1980; Tanaka and Hidaka, 1980). In this altered conformation, calmodulin can interact with a target enzyme, e.g., myosin light-chain kinase of smooth muscle (Walsh, 1985). Usually, such interaction converts the target enzyme from an inactive to an active state, triggering a cascade of biochemical reactions (often protein phosphorylations) and leading ultimately to the desired physiological response.
KeywordsBovine Brain Smooth Muscle Myosin cAMP Phosphodiesterase Chicken Gizzard Muscle Myosin Light Chain Kinase
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