Properties of Cholesterol Dissimilation by Rhodococcus equi

The identification of serum cholesterol as a risk factor in the development of coronary heart disease has resulted in attempts to reduce dietary cholesterol intake. As a result, the removal of cholesterol from food products has become a challenging research objective. We report here the loss of 40% of the cholesterol found in egg yolk preparations following treatment with sonicated extracts of Rhodococcus equi . Extracts of R. equi 21107 and R. equi 33706 removed 3.33% and 3.09% of the cholesterol from egg yolk per min per mg of crude enzyme protein, respectively. Incubation of fresh cream with R. equi 33706 extracts resulted in only a 2.4% reduction in cholesterol content (rate of reduction: 0.35% cholesterol per min per mg of protein). Cholesterol degradation by R. equi 33706 had an optimum temperature of 40°C and an optimum pH of 8.0, and there was no apparent requirement for divalent metal ions. Approximately 44% of enzyme activity was lost after a 60 min exposure at 60°C. Thin layer chromatographic analysis of cholesterol degradation products revealed only a few steroid-like compounds, primarily 4-cholesten-3-one and 1,4-cholestadiene-3-one.