The adenine portion of nicotinamide adenine dinucleotide is shown with pink fill and black letter for the atoms. The ribose portion is shown with green fill and black letters. The nicotinamide portion is shown with pink fill and blue letters. The position where hydrogen ions are added or removed is circled. Note that even though NAD in its oxidized form is written as NAD+, the molecules are both negatively charged due to the phosphate groups. NAD+ has one negative charge and NADH has 2 negative charges. Image is adapted from “Energy in living systems: Figure 1,” OpenStax College, Biology (CC BY 3.0).
Read about the biology of NAD+/NADH:
N. R. Gough, Anti-Aging Supplements: The Basis for Basis. BioSerendipity (11 June 2018) https://www.bioserendipity.com/anti-aging-supplements-the-basis-for-basishttps://www.bioserendipity.com/anti-aging-supplements-the-basis-for-basis
N. R. Gough, Anti-Aging Supplements II: NAD+ as the Key to Healthy Aging. BioSerendipity (13 June 2018) https://www.bioserendipity.com/anti-aging-supplements-ii/
N. R. Gough, Anti-Aging Supplements III: Berries and Wine for Healthy Aging. BioSerendipity (20 June 2018) https://www.bioserendipity.com/anti-aging-iii/