Possesses dinucleoside triphosphate hydrolase activity (PubMed:12574506, PubMed:15182206, PubMed:8794732, PubMed:9323207, PubMed:9576908, PubMed:9543008). Cleaves P(1)-P(3)-bis(5'-adenosyl) triphosphate (Ap3A) to yield AMP and ADP (PubMed:12574506, PubMed:15182206, PubMed:8794732, PubMed:9323207, PubMed:9576908, PubMed:9543008). Can also hydrolyze P(1)-P(4)-bis(5'-adenosyl) tetraphosphate (Ap4A), but has extremely low activity with ATP (PubMed:8794732). Exhibits adenylylsulfatase activity, hydrolyzing adenosine 5'-phosphosulfate to yield AMP and sulfate (PubMed:18694747). Exhibits adenosine 5'-monophosphoramidase activity, hydrolyzing purine nucleotide phosphoramidates with a single phosphate group such as adenosine 5'monophosphoramidate (AMP-NH2) to yield AMP and NH2 (PubMed:18694747). Exhibits adenylylsulfate-ammonia adenylyltransferase, catalyzing the ammonolysis of adenosine 5'-phosphosulfate resulting in the formation of adenosine 5'-phosphoramidate (PubMed:26181368). Also catalyzes the ammonolysis of adenosine 5-phosphorofluoridate and diadenosine triphosphate (PubMed:26181368). Modulates transcriptional activation by CTNNB1 and thereby contributes to regulate the expression of genes essential for cell proliferation and survival, such as CCND1 and BIRC5 (PubMed:18077326). Plays a role in the induction of apoptosis via SRC and AKT1 signaling pathways (PubMed:16407838). Inhibits MDM2-mediated proteasomal degradation of p53/TP53 and thereby plays a role in p53/TP53-mediated apoptosis (PubMed:15313915). Induction of apoptosis depends on the ability of FHIT to bind P(1)-P(3)-bis(5'-adenosyl) triphosphate or related compounds, but does not require its catalytic activity, it may in part come from the mitochondrial form, which sensitizes the low-affinity Ca(2+) transporters, enhancing mitochondrial calcium uptake (PubMed:12574506, PubMed:19622739). Functions as tumor suppressor (By similarity). H2O + P(1),P(3)-bis(5'-adenosyl) triphosphate = ADP + AMP + 2 H(+) adenosine 5'-phosphosulfate + H2O = AMP + 2 H(+) + sulfate adenosine 5'-phosphosulfate + NH4(+) = adenosine 5'-phosphoramidate + 2 H(+) + sulfate adenosine 5'-phosphoramidate + H2O = AMP + NH4(+) Homodimer. Interacts with UBE2I. Interacts with MDM2. Interacts with CTNNB1. Identified in a complex with CTNNB1 and LEF1. Low levels expressed in all tissues tested. Phospho-FHIT observed in liver and kidney, but not in brain and lung. Phospho-FHIT undetected in all tested human tumor cell lines. Phosphorylation at Tyr-114 by SRC is required for induction of apoptosis. A chromosomal aberration involving FHIT has been found in a lymphoblastoid cell line established from a family with renal cell carcinoma and thyroid carcinoma. Translocation t(3;8)(p14.2;q24.1) with RNF139. Although the 3p14.2 breakpoint has been shown to interrupt FHIT in its 5-prime non-coding region, it is unlikely that FHIT is causally related to renal or other malignancies. Associated with digestive tract cancers. Numerous tumor types are found to have aberrant forms of FHIT protein due to deletions in a coding region of chromosome 3p14.2 including the fragile site locus FRA3B.