PMID- 8573077
OWN - NLM
STAT- MEDLINE
DCOM- 19960301
LR  - 20190501
IS  - 0264-6021 (Print)
IS  - 1470-8728 (Electronic)
IS  - 0264-6021 (Linking)
VI  - 313 ( Pt 2)
IP  - Pt 2
DP  - 1996 Jan 15
TI  - Molecular mechanism for catalysis by a new zinc-enzyme, dopachrome tautomerase.
PG  - 447-53
AB  - Dopachrome tautomerase (DCT; EC 5.3.3.12) catalyses the conversion of 
      L-dopachrome into 5,6-dihydroxyindole-2-carboxylic acid in the mammalian 
      eumelanogenic biosynthetic pathway. This enzyme, also named TRP2, belongs to a 
      family of three metalloenzymes termed the tyrosinase-related proteins (TRPs). It 
      is well known that tyrosinase has copper in its active site. However, the nature 
      of the metal ion in the active site of DCT is under discussion. Whereas 
      theoretical predictions based on similarity between the protein sequences of the 
      TRPs suggest the presence of copper, the different inhibition pattern of DCT with 
      some metal chelators compared with that of tyrosinase suggests that the nature of 
      the metal ion could differ. Direct estimations of the metal content in purified 
      DCT preparations show the presence of around 1.5 Zn atoms/molecule and the 
      absence of copper. Apoenzyme preparation by treatment of DCT with cyanide or 
      o-phenanthroline followed by reconstitution experiments of tautomerase activity 
      in the presence of different ions confirmed that the metal cofactor for the DCT 
      active site is zinc. Our results are consistent with Zn2+ chelation by the highly 
      conserved histidine residues homologous to the histidines at the classical 
      copper-binding sites in tyrosinase. This finding accounts for the reaction 
      catalysed by DCT, i.e. a tautomerization, versus the copper-mediated oxidations 
      catalysed by tyrosinase. Based on the predicted tetrahedrical coordination of the 
      zinc ions in the enzyme active site, a molecular mechanism for the catalysis of 
      L-dopachrome tautomerization is proposed. From the present data, the existence of 
      additional ligands for metal ions other than zinc in the DCT molecule, such as 
      the proposed cysteine iron-binding sites, cannot be completely ruled out. 
      However, if such sites exist, they could be subsidiary binding sites, whose 
      function would be likely to stabilize the protein.
FAU - Solano, F
AU  - Solano F
AD  - Department of Biochemistry and Molecular Biology, School of Medicine, University 
      of Murcia, Spain.
FAU - Jimenez-Cervantes, C
AU  - Jimenez-Cervantes C
FAU - Martinez-Liarte, J H
AU  - Martinez-Liarte JH
FAU - Garcia-Borron, J C
AU  - Garcia-Borron JC
FAU - Jara, J R
AU  - Jara JR
FAU - Lozano, J A
AU  - Lozano JA
LA  - eng
PT  - Journal Article
PT  - Research Support, Non-U.S. Gov't
PL  - England
TA  - Biochem J
JT  - The Biochemical journal
JID - 2984726R
RN  - 0 (Cyanides)
RN  - 0 (Metals)
RN  - 0 (Phenanthrolines)
RN  - EC 5.- (Isomerases)
RN  - EC 5.3.- (Intramolecular Oxidoreductases)
RN  - EC 5.3.3.12 (dopachrome isomerase)
RN  - W4X6ZO7939 (1,10-phenanthroline)
SB  - IM
MH  - Amino Acid Sequence
MH  - Animals
MH  - Catalysis
MH  - Cyanides/pharmacology
MH  - *Intramolecular Oxidoreductases
MH  - Isomerases/antagonists & inhibitors/genetics/*metabolism
MH  - Metals/metabolism
MH  - Mice
MH  - Molecular Sequence Data
MH  - Phenanthrolines/pharmacology
MH  - Tumor Cells, Cultured
PMC - PMC1216928
EDAT- 1996/01/15 00:00
MHDA- 1996/01/15 00:01
PMCR- 1996/07/15
CRDT- 1996/01/15 00:00
PHST- 1996/01/15 00:00 [pubmed]
PHST- 1996/01/15 00:01 [medline]
PHST- 1996/01/15 00:00 [entrez]
PHST- 1996/07/15 00:00 [pmc-release]
AID - 10.1042/bj3130447 [doi]
PST - ppublish
SO  - Biochem J. 1996 Jan 15;313 ( Pt 2)(Pt 2):447-53. doi: 10.1042/bj3130447.