Effect of a 2-min application of various MTS reagents on subsequent [3H]adenosine uptake by oocytes expressing subsets of the TM11 Cys substitution mutants. The x-axis shows percent inhibition of subsequent [3H]adenosine uptake. Effect of 2 mm application of: A, MMTS; B, MTSEA+; C, MTSET+; D, MTSES−; E, MTS-TMR. F, effects of sequential application of MTSEA-biotin and MTS-TMR on subsequent [3H]adenosine uptake by oocytes expressing the T400C mutant PfENT1. The figure in panel F illustrates the results from one batch of oocytes. Similar results were obtained in a second batch of oocytes from a different frog.