Although deuteration is often thought to the perfect isomorphic replacement, it can lead to changes in the structure and dynamics of lipid samples, and it is necessary to consider the differences seen between the membrane structures in this context. The main isotope effect in
lipid samples is a shift in the phase transition temperature Tm, which is typically by 3–4° lower in lipids with both chains per-deuterated [52,53]. Our experiments were conducted at the yeast growth temperature of 30 °C to ensure that the membranes were in their biological fluid
state, and the deuterated membrane would indeed be somewhat more fluid than the corresponding non-deuterated membrane at the same temperature. This would typically lower the membrane thickness due to the increased disorder of the deuterated chains. The deuterated P. pastoris phospholipids however contain a significantly higher proportion of C18:1 chains (53%) than the non-deuterated samples (29%), at the same time as having fewer polyunsaturated lipids, which acts to reduce the fluidity.