Well, many enzymes and many proteins inside our body. For example, when we spoke about myoglobin and hemoglobin we saw that these proteins use metal atoms and in fact, enzymes utilize metal atoms as cofactors. Now, what's so special about these metal atoms? Well, metal atoms have the ability to lose electrons very easily. And by losing electrons, they gain a positive charge. So because they are deficient electrons, they have a positive charge.