Carbon dioxide fixation in skin

Carbon dioxide has been known for some time to be one of the products of carbohydrate metabolism. More recently it has been demonstrated that CO2 is utilized in pathways of carbohydrate synthesis. Five reactions have been described by which CO2 is incorporated into citric acid intermediates. Two important functions of CO2 fixation reactions have been suggested. Citric acid cycle intermediates can be generated by the fixation reactions and schemes utilizing two of the reaction will reverse the pyruvic kinase reaction. The latter is a step essential to glucogenesis. This paper shows that carbon dioxide fixation occurs in rat skin. The labeling pattern of oxaloacetate after fixation is consistent with patterns predicted by either the malic enzyme or propionyl carboxylase fixation reactions. The presence of the phosphopyruvic carboxykinase and pyruvic carboxylase reactions cannot be definitely ruled out by the experimental data. More work on the enzymatic level should show the significance of these various fixaon reactions in skin. Further experiments may also elucidate a relationship between factors known to affect the fixation reactions which also produce gross and microscopic changes in skin.