The Enzyme That Synthesizes Tetrahydrobiopterin from 6-Pyruvoyl-tetrahydropterin in the lemon Mutant Silkworm Consists of Two Carbonyl Reductases

• Published in: Archives of biochemistry and biophysics 2000-01, Vol.373 (2), p.442-446
• Main Authors: Iino, Teruhiko, Takikawa, Shin-Ichiro, Yamamoto, Toshio, Sawada, Hiroshi
• Format: Article
• Language: English
• Subjects: Alcohol Oxidoreductases; Alcohol Oxidoreductases - isolation & purification; Alcohol Oxidoreductases - metabolism; analogs & derivatives; Animals; biopterin; Biopterins; Biopterins - analogs & derivatives; Biopterins - biosynthesis; biosynthesis; biosynthesis of tetrahydrobiopterin; Bombyx; Bombyx - enzymology; Bombyx mori; carbonyl compounds; carbonyl reductase; enzymology; Insect Proteins; Insect Proteins - isolation & purification; isolation & purification; lemon mutant silkworm; metabolism; Molecular Structure; oxidoreductases; Pterins; Pterins - metabolism; sepiapterin reductase; tetrahydrobiopterin
• ISSN: 0003-9861; 1096-0384
• DOI: 10.1006/abbi.1999.1561

Tetrahydrobiopterin plays an important role in the biosynthesis of certain neurotransmitters. Using DEAE–Sepharose FF column chromatography, we separated the enzyme that synthesizes tetrahydrobiopterin from 6-pyruvoyl-tetrahydropterin [which is different from sepiapterin reductase (EC 1.1.1.153)] in the lemon mutant of the silkworm Bombyx mori into two fractions, which were named carbonyl reductase I (CR I) and carbonyl reductase II (CR II). The CR I enzyme converted 6-pyruvoyl-tetrahydropterin to 6-lactoyl-tetrahydropterin, while CR II converted 6-pyruvoyl-tetrahydropterin to 1′-hydroxy-2′-oxopropyl-tetrahydropterin, both reactions occurring only in the presence of NADPH. Neither of the two carbonyl reductases alone was able to catalyze the conversion of 6-pyruvoyl-tetrahydropterin to tetrahydrobiopterin in the presence of NADPH. However, when CR I was mixed with CR II in the reaction mixture, 6-pyruvoyl-tetrahydropterin was reduced to tetrahydrobiopterin in the presence of NADPH. Moreover, CR I catalyzed the formation of tetrahydrobiopterin from 1′-hydroxy-2′-oxopropyl-tetrahydropterin, while CR II converted 6-lactoyl-tetrahydropterin to tetrahydrobiopterin, both reactions occurring only in the presence of NADPH. Our results suggest that there are two potential routes for formation of tetrahydrobiopterin from 6-pyruvoyl-tetrahydropterin in the lemon mutant silkworm. In the first route, 1′-hydroxy-2′-oxopropyl-tetrahydropterin is formed from 6-pyruvoyl-tetrahydropterin by CR II and then reduced to tetrahydrobiopterin by CR I, both reactions occurring only in the presence of NADPH. In the other route, 6-pyruvoyl-tetrahydropterin is reduced to 6-lactoyl-tetrahydropterin by CR I and then converted to tetrahydrobiopterin by CR II, both reactions occurring only in the presence of NADPH.