Figure 1.

Hypothesis for how segregating metabolic processes among different cell types could accelerate substrate consumption. Consider a metabolic pathway where a primary substrate (S) is transformed by an enzyme (E_s) into an intermediate (I). The intermediate is then further transformed by another enzyme (E_I) into an end product (P). (a) If E_S and E_I compete for the same finite pool of an intracellular resource and E_S has preferential access to that resource, then I will accumulate at early times and only be consumed at later times. (b) The consequence is the transient accumulation of I. (c) Conversely, if E_S and E_I are segregated into different cell types, then competition is eliminated and E_I has increased access to the intracellular resource. (d) The consequence is the increased consumption and reduced accumulation of I.