Hydrolyzes certain amino acid conjugates of the plant growth regulator indole-3-acetic acid (IAA), including IAA-Phe, IAA-Leu and IAA-Tyr (PubMed:7792599, PubMed:10072397, PubMed:11923288). Can also use IAA-Ala, IAA-Gly, IAA-Met and IAA-Glu as substrates with low efficiency (PubMed:7792599, PubMed:10072397, PubMed:11923288). No activity with IAA-Ile, IAA-1-O-beta-D-glucose or IAA-myo-inositol (PubMed:7792599, PubMed:10072397, PubMed:11923288). Is the most efficient enzyme of the ILL family for IAA-Leu hydrolysis (PubMed:11923288). Important for IAA-Leu and IAA-Phe hydrolysis in roots (PubMed:15155875). May act with ILL2 to provide free IAA to germinating seedlings (PubMed:15155875). Manganese and/or Cobalt or Copper. The ion enhances activity. kcat is 0.017 sec(-1) with IAA-Ala as substrate. kcat is 0.070 sec(-1) with IAA-Leu as substrate. Optimum pH is 7.5. Expressed in leaves, stems, siliques, seeds and flowers. Detected in central regions of cotyledons, hypocotyl, radicle of mature embryos and seedlings, micropyle of siliques and in pollen. Belongs to the peptidase M20 family.