The　Glutamine　transfer　system　consists　of　three　components:　glutamine　binding　protein　(GlnBP),　the　transmembrame　receptor　(TMR)　and　the　ATP　binding　subunit.　it　is　typical　of　periplasmic　transfer　systems　in　Escherichia　coli　and　belongs　to　the　ABC　(ATP-binding　cassettes)　super　family.　Until　now,　the　mechanism　of　glutamine　release　from　its　receptor　remains　unknown,　also　little　information　is　available　on　the　interactions　between　the　substrate-bound　complex　and　the　TMR　because　of　a　lack　of　structure　information　of　the　TMR.　In　our　study,　a　steered　molecular　dynamics　(SMD)　method　is　used　to　explore　the　possible　pathway　for　glutamine　release　from　its　receptor　GlnBP.　It　is　found　that　a　novel　back-door　pathway,　rather　than　a　front-door　pathway　is　more　reasonable.　This　work　may　help　understand　the　substrate　release　mechanism　of　the　periplasmic　transfer　system　and　additionally　give　some　clues　as　to　how　the　substrate-bound　complex　binds　to　its　TMR　and　completes　the　subsequent　translocation　of　the　substrate.　(c)　2009　Published　by　Elsevier　B.V.