Final answer:
Nucleotide hydrolysis, such as that of ATP or GTP, changes binding affinities between protein subunits by causing conformational changes and can release energy for cellular processes. GTP hydrolysis leads to reassociation of G-protein subunits, and ATP hydrolysis changes myosin's interaction with actin in muscle contraction.
Step-by-step explanation:
Nucleotide hydrolysis, such as that of ATP and GTP, is a crucial biological reaction that affects the binding affinity between subunits in various molecular complexes. For instance, when GTP hydrolysis occurs, the alpha subunit of a G-protein converts GTP back to GDP. This hydrolysis causes the alpha subunit to assume an inactive form, which then prefers to reassociate with the beta and gamma subunits. A similar process occurs with ATP in muscle contraction, where ATP binding to myosin leads to the release of actin, after which ATP is hydrolyzed, allowing the myosin head to attain a 'cocked' position, ready for further interaction once actin binding sites become available.
The hydrolysis reactions of these nucleotides are not only related to changes in binding affinities but are also significant in providing the energy required for various cellular processes. ATP hydrolysis, in particular, releases a substantial amount of energy due to the relief of repulsion between the negatively charged phosphate groups. This energy can be utilized for phosphorylation of other molecules, thereby altering their activity and interactions.