text: Fibrillin-1 contains a type of epidermal growth factor-like domain which binds to this element.
full_question: Fibrillin-1 contains a type of epidermal growth factor-like domain which binds to this element. Low levels of this element can be indicated by tightening a blood pressure cuff on the brachial artery, which leads to a carpal spasm called the "hand of the obstetrician." Levels of this element in cells can be measured using aequorin. This element regulates the binding of phospholipids to annexins. This element can become deficient in the blood of patients with many blood transfusions since it complexes to citrate in serum. Along with diacylglycerol, this element activates protein kinase C. Parvalbumin contains three helix-loop-helix domains which bind to this element. Levels of this element in serum can be reduced by a hormone produced by the parafollicular cells of the thyroid gland or raised by parathyroid hormone. This element binds to troponin, which allows myosin to bind to actin, causing the sarcomere to contract. For 10 points, name this element which regulates muscle contraction and supports bone health.
first_sentence: Fibrillin-1 contains a type of epidermal growth factor-like domain which binds to this element.
raw_answer: calcium [or Ca]