A stack plot of the 13 C NMR spectra for the two experiments carried out in the presence of cells is shown in Fig. . In the experiment with intact cells, fumarate transport across the cell membrane is slow relative to 𝑇 , so no malate signal is detected. In the experiment with lysed cells, the fumarate has access to the enzyme and reacts with water to form malate. The asymmetry of this molecule means the 13 The fumarate and malate peak integrals are plotted in Fig. , and a fit to the data is obtained using a kinetic model that only includes fumarate conversion to malate, and relaxation of both species: 𝐹 → 𝑀.