Although no heterotrophs use carbon dioxide in biosynthesis, some carbon dioxide is incorporated in their metabolism. Notably pyruvate carboxylase consumes carbon dioxide (as bicarbonate ions) as part of gluconeogenesis, and carbon dioxide is consumed in various anaplerotic reactions. 
6-phosphogluconate dehydrogenase catalyzes the reductive carboxylation of ribulose 5-phosphate to 6-phosphogluconate in E. coli under elevated CO concentrations.