MODEL #2 NARRATIVE. “Metabolic systems can be viewed as complex traits, because individual metabolic enzymes in isolation are rarely pertinent to in vivo physiology until they become part of an organized metabolic pathway. Extant metabolic pathways in general contain a set of enzymes catalyzing sequential reactions in a highly concerted manner.”
http://onlinelibrary.wiley.com/doi/10.1111/nph.12416/full