Troponin
(tro-po'-nin) is a complex of proteins that is integral
to muscle contraction. Troponin is attached to tropomyosin
(another type of protein) and lies within the groove between
actin (muscle)filaments. In a relaxed muscle, tropomyosin
blocks the attachment of cross bridges to actin, thus
preventing contraction. When the muscle cell is stimulated
to contract, mechanisms cause the concentration of calcium
in the sarcoplasm to rise. Some of this calcium attaches
to troponin, causing a conformational change that moves
troponin and tropomyosin out of the way so that the cross
bridges can attach to actin and produce muscle contraction.
Without troponin, there can be no muscular contraction.
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