Updated project metadata. Auxin is a pivotal plant hormone that controls virtually all aspects of plant growth and development. Auxin is transported in plants in a polar fashion and PIN-FORMED (PIN) transporters are the key players in this process. Canonical PINs possess a long cytosolic loop that is subject to regulation by AGC1 and AGC3 kinases. To characterize the transporters, they are expressed in Xenopus laevis oocytes alone or with the different activating kinases. Since transport rates always depend on the amount of active transporter in the membrane it is paramount to ensure that the levels of transporter, kinase and degree of phosphorylation are similar to be able to compare transport rates directly. To this end we expressed PIN1, PIN2 and PIN3 either alone or with D6PK (an AGC1 kinase) or PID (an AGC3 kinase) in oocytes. The protein levels and the degree of phosphorylation of the loop were established and found to be comparable between PINs.