Two stable fluorescent derivatives of molybdopterin have been structurally characterized. Form A is an oxidized pterin with a 6-alkyl substituent. Results of chemical, mass spectral, and NMR studies are consistent with the side chain formulation -C≡C-CH-OHCH2OPO32-. Similar studies on the Form B derivative indicate that it is the phosphorylated analog of urothione but lacks the 3-methylthio function. Form B (dephospho) can be synthesized from urothione by desulfuration with Raney nickel and oxidation with SeO2. Chicken liver sulfite oxidase (sulfite:ferricytochrome c oxidoreductase, EC 22.214.171.124) contains one phosphate residue (as molybdopterin) per subunit. The phosphate is noncovalently bound but is not released by trichloroacetic acid at 4°C. The yield of Form A and Form B from sulfite oxidase is 0.50 and 0.27/subunit, respectively. The phosphate ester bond in isolated molybdopterin (Form B) is partially hydrolyzed by 1 N HCl at 100°C (33% in 1 h). The release of inorganic phosphate from sulfite oxidase was more rapid (35% in 10 min) due to the presence of molybdate in the denatured enzyme mixture but slower than expected from a high energy phosphate bond. The presence of molybdopterin in a wide variety of molybdenum- and tungsten-containing enzymes has been demonstrated. Glucose oxidase and the iron and manganese superoxide dismutases are devoid of molybdopterin.
|Original language||English (US)|
|Number of pages||9|
|Journal||Journal of Biological Chemistry|
|State||Published - Jan 1 1984|
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology