The use of citric acid in the Mag-Cal Citrate formula makes the minerals highly soluble and bioavailable. Taking the two minerals together also facilitates absorption. Biologically, magnesium and calcium are intimately interlocked. In some reactions, such as synthesis of nucleic acids and protein, calcium and magnesium are antagonistic. Magnesium is necessary for these processes, while calcium inhibits them, thus, it plays a regulatory role. Magnesium and calcium collaborate, however, in the production of adenosine triphosphate (ATP). Magnesium appears to regulate the gate through which calcium enters into cells to switch on such vital functions as heartbeat. Magnesium is necessary to bind calcium for the formation of hard tooth enamel. Both minerals are important in bone formation and muscular contractions.