The Ca++ ions released during a muscle fiber contraction attach with:

Explanation

Ca2+ ions attach to troponin during muscle fiber contraction. Troponin is a regulatory protein complex found on the actin filaments in muscle fibers. When Ca2+ ions bind to troponin, it induces a conformational change that moves tropomyosin away from the binding sites on actin, allowing myosin to bind and initiate muscle contraction.