TY - JOUR
T1 - Wild-type phenylalanine hydroxylase activity is enhanced by tetrahydrobiopterin supplementation in vivo
T2 - ASHG 2004 Meeting Toronto
AU - Kure, Shigeo
AU - Sato, Kenichi
AU - Fujii, Kunihiro
AU - Aoki, Yoko
AU - Suzuki, Yoichi
AU - Kato, Seiichi
AU - Matsubara, Yoichi
N1 - Funding Information:
This work was supported by grants from the Ministry of Education, Science, Sports and Culture and the Ministry of Health and Public Welfare, Japan.
PY - 2004/9
Y1 - 2004/9
N2 - We previously proposed a novel disease entity, tetrahydrobiopterin (BH 4)-responsive phenylalanine hydroxylase (PAH) deficiency, in which administration of BH 4 reduced elevated levels of serum phenylalanine [J. Pediatr. 135 (1999) 375-378]. Subsequent reports indicate that the prevalence of BH 4-responsive PAH deficiency is much higher than initially anticipated. Although growing attention surrounds treatment with BH 4, little is known about the mechanism of BH 4 responsiveness. An early report indicates that BH 4 concentration in rat liver was 5 μM where K m for BH 4 of rat PAH was estimated to be 25 μM in an oxidation experiment using a liver slice, suggesting relative insufficiency of BH 4 in liver in vivo. In the present study, we developed a breath test for mice using [1- 13C] phenylalanine in order to examine the BH 4 responsiveness of normal PAH in vivo. The reliability of the test was verified using BTBR mice and its mutant strain lacking PAH activity, Pah enu2. BH 4 supplementation significantly enhanced 13CO 2 production in C57BL/6 mice when phenylalanine was pre-loaded. Furthermore, BH 4 apparently activated PAH in just 5 min. These observations suggest that submaximal PAH activity occurs at the physiological concentrations of BH 4 in vivo, and that PAH activity can be rapidly enhanced by supplementation with BH 4. Thus, we propose a possible hypothesis that the responsiveness to BH 4 in patients with PAH deficiency is due to the fact that suboptimal physiological concentrations of BH 4 are normally present in hepatocytes and the enhancement of the residual activity may be associated with a wide range of mutations.
AB - We previously proposed a novel disease entity, tetrahydrobiopterin (BH 4)-responsive phenylalanine hydroxylase (PAH) deficiency, in which administration of BH 4 reduced elevated levels of serum phenylalanine [J. Pediatr. 135 (1999) 375-378]. Subsequent reports indicate that the prevalence of BH 4-responsive PAH deficiency is much higher than initially anticipated. Although growing attention surrounds treatment with BH 4, little is known about the mechanism of BH 4 responsiveness. An early report indicates that BH 4 concentration in rat liver was 5 μM where K m for BH 4 of rat PAH was estimated to be 25 μM in an oxidation experiment using a liver slice, suggesting relative insufficiency of BH 4 in liver in vivo. In the present study, we developed a breath test for mice using [1- 13C] phenylalanine in order to examine the BH 4 responsiveness of normal PAH in vivo. The reliability of the test was verified using BTBR mice and its mutant strain lacking PAH activity, Pah enu2. BH 4 supplementation significantly enhanced 13CO 2 production in C57BL/6 mice when phenylalanine was pre-loaded. Furthermore, BH 4 apparently activated PAH in just 5 min. These observations suggest that submaximal PAH activity occurs at the physiological concentrations of BH 4 in vivo, and that PAH activity can be rapidly enhanced by supplementation with BH 4. Thus, we propose a possible hypothesis that the responsiveness to BH 4 in patients with PAH deficiency is due to the fact that suboptimal physiological concentrations of BH 4 are normally present in hepatocytes and the enhancement of the residual activity may be associated with a wide range of mutations.
KW - BTBR mouse
KW - CO analysis
KW - Enzyme activity
KW - In vivo activity
KW - Pah mouse
KW - Phenylalanine pre-loading
UR - http://www.scopus.com/inward/record.url?scp=4744342508&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=4744342508&partnerID=8YFLogxK
U2 - 10.1016/j.ymgme.2004.06.016
DO - 10.1016/j.ymgme.2004.06.016
M3 - Conference article
C2 - 15464429
AN - SCOPUS:4744342508
VL - 83
SP - 150
EP - 156
JO - Biochemical Medicine and Metabolic Biology
JF - Biochemical Medicine and Metabolic Biology
SN - 1096-7192
IS - 1-2
Y2 - 26 October 2004 through 26 October 2004
ER -