The purP gene for energized high-affinity adenine uptake in Escherichia coli is localized to a restriction fragment between tnaB and bglR. Comparison with DNA sequence data (Burland et al. 1993) indicates the involvement of the open-reading frame f445 (86003 < 84666). A non-energized transport route of lower affinity also occurs. The purP system is known to require metabolic removal of transported adenine which would diminish futile cycling by the two transport systems and toxicity by external adenine. Analysis of a conventional kinetic model for permeases suggests that internal adenine might inhibit transport sufficiently to account for the lack of accumulation.