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Recombinant Human Tyrosine Hydroxylase Types 1–4 Show Regulatory Kinetic Properties for the Natural (6R)-Tetrahydrobiopterin Cofactor1

Authors :
Hiroyoshi Hidaka
Hiroshi Ichinose
Shamima Nasrin
Toshiharu Nagatsu
Source :
The Journal of Biochemistry. 116:393-398
Publication Year :
1994
Publisher :
Oxford University Press (OUP), 1994.

Abstract

Human tyrosine hydroxylase (hTH) exists in four isoforms. The four recombinant hTH isoenzymes types 1-4 (hTH1-4) produced in and purified from Escherichia coli showed regulatory kinetic properties for the natural (6R)-L-erythro-tetrahydrobiopterin (RBPH4) as a cofactor. In contrast, the unnatural cofactor (6S)-L-erythro-tetrahydrobiopterin (SBPH4) and a synthetic cofactor (6RS)-methyl-tetrahydropterin (6MPH4) showed usual kinetic characteristics with each of hTH1-4. Substrate inhibition by tyrosine was observed for each of hTH1-4 with natural RBPH4. Two different Km values for pterin cofactor were observed at a high concentration (200 microM) of L-tyrosine only with natural RBPH4, in contrast to a single Km value for unnatural SBPH4 or synthetic 6MPH4. The present results suggest that in the presence of relatively high concentrations (approximately 100 microM) of tyrosine in vivo, RBPH4 cofactor may have a regulatory role for the activity of all four human isoenzymes in vivo. We also found that recombinant hTH1 and 3 were more unstable than hTH2 and 4, suggesting that the 4-amino-acid insertion in hTH2 and 4 may be responsible for the relative stability of hTH2 and 4 isoenzymes.

Details

ISSN :
17562651 and 0021924X
Volume :
116
Database :
OpenAIRE
Journal :
The Journal of Biochemistry
Accession number :
edsair.doi...........6f055ccfe684d4101cbf179d00537b7c
Full Text :
https://doi.org/10.1093/oxfordjournals.jbchem.a124537