Final answer:
The amino acid that interacts with Mg2+ is arginine, playing a critical role in the synthesis of arginosuccinate in the urea cycle with Mg2+ acting as a cofactor.
Step-by-step explanation:
The amino acid that interacts with Mg2+ is arginine. In one of the key steps of the urea cycle, specifically the synthesis of arginosuccinate, arginine plays a critical role where Mg2+ acts as a cofactor. Arginine is not a negatively charged amino acid; rather, it is positively charged due to its side chain, which can bind to a negatively charged molecule such as glutamate. This interaction allows the enzyme arginosuccinate synthase to catalyze the reaction by combining citrulline and aspartate to form arginosuccinate, a process that necessitates ATP and the presence of Mg2+, highlighting the importance of this cofactor in amino acid metabolism and protein synthesis.