오옥신 전달억제물질로 알려진 2,3,5-triiodobenzoic acid (TIBA)는 황화녹두 하배축 조직에서 오옥신유도 에틸렌 생성을 억제하였으며, 이러한 억제는 오옥신 전달억제와는 관련이 없다는 것을 알게되었다. 이 억제물질은 에틸렌 바로 전단계 중간대사물인 1-aminocyclopropane-1-carboxylic acid(ACC)에 의한 에틸렌 생성도 비슷한 양상으로 억제 시켰으며 또 조직에서 ACC의 축적을 증가시켰다. 이러한 사실은 TIBA가 ACC에서 에틸렌으로 전환되는 과정을 특정하게 억제한다는 것을 시사하고 있다. TIBA 가 free radical scavenger로서 작용할 가능성은 luminol chemiluminescene의 실험 결과 배제되었다. Mercaptoethanol을 이용한 실험결과는 TIBA가 ethylene forming enzyme에 sulfhydryl 억제제로 작용한다는 가능성을 뒷받침 하고있다.
Auxin-induced ethylene production in hypocotyl segments of etiolated mung bean seedlings was severely inhibited by 2,3,5-triiodobenzoic acid (TIBA), a potent inhibitor of auxin transport. However. the inhibition of ethylene biosynthesis by the transport inhibitor was found to be unrelated to an obvious impairment of the auxin transport system. The inhibitor also suppressed ethylene production from segments fed with 1-aminocyclopropane-1-carboxylic acid (ACC). the immediate precursor of ethylene. TIBA treatment also led to a substantial accumulation of ACC in the tissue incubated with either auxin or ACC. These findings suggest that TIBA inhibits ethylene production by specifically blocking the conversion of ACC to ethylene. The possibility of TIBA acting as a free radical scavenger was ruled out by the lack of TIBA effect on chemiluminescence in a luminol-based system in vitro. Results obtained from experiments with mercaptoethanol suggest that TIBA may act as a sulfhydryl inhibitor on "ethylene forming enzyme (EFE)", the enzyme catalyzing the formation of ethylene from the penultimate precursor, ACC.
