ABSTRACT
This chapter examines types of connections that exist between metabolic pathways, offering examples of three distinct types. The first of these is the connection of gluconeogenesis to glycolysis. The second is a sharing of just one intermediate, the case of connection of glycolysis with glycogen metabolism. The third connectivity is the parallel connections of mobile cofactors. However, the principle that emerges from others is that metabolic connections require release of intermediary metabolites, as was the case with aconitase and xanthine oxidase. For example, perhaps the use of nicotinamide adenine dinucleotide as part of the reaction produced a reaction that has a more favorable equilibrium position than simple hydrolysis for that reaction under metabolic conditions. Closely related to the notion of compartmentation as an explanation of metabolic anomalies is the idea that diffusion limitations exist to prevent mixing. Diffusion was developed in the mid-nineteenth century by Fick, based upon heat convection ideas formulated by Fourier.
