I.U.B.:1.1.1.51and1.1.1.50

Hydroxysteroiddehydrogenasescatalyzetheinterconversionofhydroxylandcarboxylgroupsofsteroids.P.testosteroniderivedhydroxysteroiddehydrogenasesareoftwotypes:3-α-hydroxysteroiddehydrogenase(αenzyme)and3-β-hydroxysteroiddehydrogenase(βenzyme).Theαenzymehasamolecularweightof47,000daltons.Theαenzymeoxidizesonly3-α-hydroxysteroidsoftheC19,C21andC24series.Itisinhibitedbyheavymetalsandsulfhydryl-bindingagents.Theβenzymecatalyzestheoxidationof3-β-hydroxysteroidsoftheC19andC21series,17-β-hydroxysteroidsoftheC18,C19andC21series,aswellascertain16-β-hydroxysteroids.Itisinhibitedbyheavymetalsandreducingagents.Theoxidationoftestosteroneisinhibitedby3,17-α-estrADIolandother1,3,5-estradienederivatives.Worthingtonsuppliestwopreparations:onefromtheregularP.testosteroni(ATCC11966)culturewhichproducesboththeαandtheβenzymes,andasecondfromamutantstrainwhichproducesalmostexclusivelytheαenzyme.Byusingboth,theβ-hydroxysteroidcanbedeterminedbydifference.

TechnicalNote:STDHPandSTDHcontainbothαandβactivities.STDHMP,however,containsonlyαactivity.

UnitDefinition:OneUnitreducesonemicromoleofNADperminuteat25°C,pH9.0usingandrosteroneortestosteroneassubstrate.