Acts on tyrosine phosphorylated proteins, low-MW aryl phosphates and natural and synthetic acyl phosphates with differences in substrate specificity between isoform 1 and isoform 2. Does not possess phosphatase activity. H2O + O-phospho-L-tyrosyl-[protein] = L-tyrosyl-[protein] + phosphate H2O + O-phospho-L-tyrosyl-[protein] = L-tyrosyl-[protein] + phosphate a phosphate monoester + H2O = an alcohol + phosphate a phosphate monoester + H2O = an alcohol + phosphate Inhibited by sulfhydryl reagents. Interacts with EPHA2; dephosphorylates EPHA2. Interacts with EPHB1. Interacts with the SH3 domain of SPTAN1. There is no interaction observed for isoforms 2 or 3. The ratio of isoform 1 to isoform 2 is 2:1 in allele A, 4:1 in allele B and 1:4 in allele C. Expressed in T-lymphocytes. Phosphorylated by LCK (PubMed:9038134, PubMed:10336608). Phosphorylation at Tyr-132 increases its phosphatase activity (PubMed:9038134). Not phosphorylated. ACP1 is genetically polymorphic. Three common alleles are known in Caucasians: ACP1*A, ACP1*B and ACP1*C. They give rise to six different phenotypes. Each allele appears to encode two electrophoretically different isozymes, F and S, which are produced in allele-specific ratios (PubMed:1939112). The sequence shown is that of allele ACP1*B and allele ACP1*C. Belongs to the low molecular weight phosphotyrosine protein phosphatase family.