So far there are six SUMO proteases in humans that have been designated SENP1-3 and SENP5-7 (sentrin/SUMO-specific protease).1 The six proteases possess a conserved C-terminal domain which are variable in size, and with a distinct N-terminal domain between them. The C-terminal domain shows catalytic activity and N-terminal domain regulates cell localization and substrate specificity.
SENP1 (Sentrin-specific protease 1) is a human protease of 643 amino acids with a weight of 73 kDa, EC number in humans 3.4.22.B70, which adopts a conformation that identifies it as a member of the superfamily of cysteine proteases contain a catalytic triad with characterized three amino acids: a cysteine at position 602, a histidine at position 533 and aspartic acid at position 550. The important nucleophile is cysteine located at the N-terminal alpha helix of the protein core, the other two amino acids, aspartate and histidine, are located in a beta sheet end. 
SENP1 The catalytic site consists of three amino acids: Cys 602, His 533 and Asp 550.
Both SENP1 are located in the nucleus and cytosol depending on the cell type, although it has been seen that is exported out from the nucleus to the cytosol through a sequence of nuclear export (NES) that is located at the C-terminus. The mammalian SENP1 is localized mainly in the nucleus.
SENP1 catalyzes maturation SUMO protein (small ubiquitin-related modifier), which causes hydrolysis peptide bond of SUMO is in a conserved sequence Gly-Gly-|-Ala-Thr-Tyr at the C-terminal  to be added to the conjugation of other proteins (sumoylation). In vertebrates there are three members of the family of SUMO: SUMO-1, -2 and -3. SENP1 can catalyze any of these three. This conjugation of SUMO toward other proteins is a lot like ubiquitination, however these modifications leads to different results depending on the type of protein been modified.
^Gong L, Millas S, Maul GG, Yeh ET (Feb 2000). "Differential regulation of sentrinized proteins by a novel sentrin-specific protease". The Journal of Biological Chemistry. 275 (5): 3355–9. doi:10.1074/jbc.275.5.3355. PMID10652325.
^Bailey D, O'Hare P (Jan 2004). "Characterization of the localization and proteolytic activity of the SUMO-specific protease, SENP1". The Journal of Biological Chemistry. 279 (1): 692–703. doi:10.1074/jbc.M306195200. PMID14563852.
^Kim YH, Sung KS, Lee SJ, Kim YO, Choi CY, Kim Y (2005). "Desumoylation of homeodomain-interacting protein kinase 2 (HIPK2) through the cytoplasmic-nuclear shuttling of the SUMO-specific protease SENP1". FEBS Letters. 579 (27): 6272–6278. doi:10.1016/j.febslet.2005.10.010. PMID16253240.
Mikolajczyk J, Drag M, Békés M, Cao JT, Ronai Z, Salvesen GS (Sep 2007). "Small ubiquitin-related modifier (SUMO)-specific proteases: profiling the specificities and activities of human SENPs". The Journal of Biological Chemistry. 282 (36): 26217–24. doi:10.1074/jbc.M702444200. PMID17591783.
Drag M, Mikolajczyk J, Krishnakumar IM, Huang Z, Salvesen GS (Jan 2008). "Activity profiling of human deSUMOylating enzymes (SENPs) with synthetic substrates suggests an unexpected specificity of two newly characterized members of the family". The Biochemical Journal. 409 (2): 461–9. doi:10.1042/BJ20070940. PMID17916063.
Veltman IM, Vreede LA, Cheng J, Looijenga LH, Janssen B, Schoenmakers EF, Yeh ET, van Kessel AG (Jul 2005). "Fusion of the SUMO/Sentrin-specific protease 1 gene SENP1 and the embryonic polarity-related mesoderm development gene MESDC2 in a patient with an infantile teratoma and a constitutional t(12;15)(q13;q25)". Human Molecular Genetics. 14 (14): 1955–63. doi:10.1093/hmg/ddi200. PMID15917269.
Kim YH, Sung KS, Lee SJ, Kim YO, Choi CY, Kim Y (Nov 2005). "Desumoylation of homeodomain-interacting protein kinase 2 (HIPK2) through the cytoplasmic-nuclear shuttling of the SUMO-specific protease SENP1". FEBS Letters. 579 (27): 6272–8. doi:10.1016/j.febslet.2005.10.010. PMID16253240.