Growth temperature-dependent stearoyl coenzyme A desaturase activity of Fusarium oxysporum microsomes

The characteristics of the microsomal stearoyl CoA desaturase (EC 1.14.99.5) of vegetative Fusarium oxysporum cells grown at different temperatures were studied. The enzyme had an unusual preference for NADPH (Km = 38 μM) over NADH (Km = 89 μM) as electron donor, and a relatively high optimum pH of 8.3. Enzyme activity was highest in microsomes from cells grown at 37 °C and lowest in cells grown at 15 °C. This result correlated well with the observed changes in oleic acid content of the microsomal lipids.Both NADPH-linked reductase activities and hemoprotein content were lowest in cells grown at 37 °C. Spectrophotometric analysis of the microsomal hemoproteins indicated the absence of cytochrome b5 and the presence of a b-type heme with a pyridine hemochrome α band absorption maximum at 565 nm. Labile sulfide analysis and inhibitor studies with thenoyltrifluoroacetone suggested a role for an iron–sulfur protein in the electron transfer system associated with the desaturase.