Final answer:
The researcher should study troponin and myosin to understand the relationship between Ca2+ binding proteins and muscle relaxation speed, as these proteins play key roles in muscle contraction and relaxation.
Step-by-step explanation:
To investigate the relationship between Ca2+ binding proteins and the speed of relaxation in muscle tissue, the researcher should study proteins such as troponin and myosin. These are key elements in the mechanism of muscle contraction and relaxation. Calcium ions (Ca2+) combine with troponin in the troponin-tropomyosin complex to facilitate the contraction of muscles by removing the inhibition on myosin heads, thus enabling them to form cross-bridges with actin. For relaxation to occur, Ca2+ is removed, which leads to the re-shielding of the actin-binding sites. In smooth muscles, which lack troponin, the protein calmodulin regulates cross-bridge formation instead. An increased understanding of these proteins and their interaction with calcium could provide valuable insights into the physiological processes of muscle relaxation.