Production, isolation and characterization of a sterol esterase from Ophiostoma piceae

We studied extracellular sterol esterase production by the ascomycete Ophiostoma piceae in liquid culture. Esterase activity was found in low levels in glucose medium but it was strongly induced by olive oil. An esterase was purified from the 0.5% olive oil-supplemented cultures using ultrafiltration followed by a single chromatographic step on a hydrophobic interaction column. The enzyme was a glycoprotein with 8% N-linked carbohydrate content, a molecular mass by SDS/PAGE around 56.5 kDa and an isoelectric point of 3.3. Its N-terminal sequence was TTVNVKYPEGEVV. Substrate specificity studies showed that the O. piceae esterase hydrolyzes p-nitrophenol esters, tributyrin, triolein and different cholesterol esters. Both affinity (Km) and catalytic constant (k(cat)) were positively affected by the length of the fatty acid esterifying glycerol and cholesterol. The presence of double bonds in the acyl chain increased the enzyme efficiency, although it affected the k(cat) values rather than the Km on the cholesterol esters. The O. piceae enzyme showed no interfacial activation. This enzyme could have biotechnological applications in paper manufacturing since it efficiently hydrolyzes both triglycerides and sterol esters, which form pitch deposits during manufacturing of softwood and hardwood paper pulps, respectively.