The SARS-CoV2 pandemic has resulted in a huge increase in research focusing on the SARS-CoV2 Spike protein interaction with the human ACE2 receptor. This interaction drives viral infection and transmission and is a vaccine and therapeutic target. In vitro biophysical studies, such as SPR, rely on recombinantly expressed protein to model the protein interactions that occur in vivo. In this study I demonstrate that the choice of expression system can impact the affinity and kinetics of the interaction when measured with the Biacore S200. Human ACE2 proteins expressed in mammalian cells showed an almost ten-fold increase in affinity to various SARS-CoV2 Spike proteins compared to hACE2 expressed in yeast. Expression system, therefore, may influence experimental outcomes and should be carefully considered at the beginning of each project.