NAD+ is a crucial coenzyme found in all living cells, acting as an electron carrier in redox reactions and playing a key role in cellular metabolism. ItNAD+ is a crucial coenzyme found in all living cells, acting as an electron carrier in redox reactions and playing a key role in cellular metabolism. ItNAD+ is a crucial coenzyme found in all living cells, acting as an electron carrier in redox reactions and playing a key role in cellular metabolism.