JBC, Vol. 254, Issue 11, 4349-4351, Jun, 1979
The stereochemistry of NADH utilization by the flavoenzyme monooxygenase orcinol hydroxylase
C. C. Ryerson and C. Walsh
Ribbons et al. (Ribbons, D.W., Ohta, Y., and Higgins, I.J. (1972) in
Molecular Basis of Electron Transport, Miami Winter Symposic Series
(Schultz, J., and Cameron, B.F., eds) Vol. 4, pp. 251-274, Academic Press,
New York) presented a preliminary report that the flavoenzyme monooxygenase
orcinol hydroxylase shows mixed type 4R, 4S stereospecificity with respect
to dihydronicotinamide oxidation when resorcinol and m-cresol were used as
substrate analogs. With the natural substrate orcinol, 4R chirality was
maintained. In kinetic isotope experiments reported here, we demonstrate in
fact that orcinol hydroxylase maintains 4R stereospecificity with respect
to dihydronicotinamide oxidation with all three substrates, orcinol,
resorcinol, and m-cresol. Deuterium and tritium kinetic isotope effects
were detected under Vmax conditions with (4R)-[4-2H]-, and (4R)-[4-3H]NADH
for all three substrates. No isotope effect was observed with
(4S)-[4-2H]NADH and tritium labilization from assays with (4S)-[4-3H]-NADH
was negligible in all cases.