Disclosed is a family of P450 monooxygenases, each member of which regioselectively oxidizes avermectin to 4''-keto-avermectin. The P450 monooxgenases find use in methods and formulations for making emamectin from avermectin. Also disclosed are methods for purifying the P450 monooxygenases of the invention, binding agents that specifically bind to the P450 monooxygenases of the invention, and genetically engineered cells that express the P450 monooxygenases of the invention. Also disclosed are ferredoxins and ferredoxin reductases that are active with the P450 monooxygenases of the invention.