Properties of Chitin Synthetase in Isolated Chitosomes from Yeast Cells of Mucor rouxii*

Chitin synthetase was isolated and purified 120-fold from the supernatant fraction (54,500 x g) of broken yeast cells of Mucor rouxii. The purified preparations consisted mainly of chitin synthetase particles (chitosomes) with an average size larger than 7 x 10” daltons (by gel filtration) and an average sedimentation coefficient of 105 S. The samples also contained other enzyme complexes (fatty acid synthetase, pyruvate dehydrogenase, and, depending on method, ribosomes). Nearly all of the chitosomal chitin synthetase occurred in a zymogenic form that required proteolytic activation. In most properties, the chitosomal enzyme was similar to crude enzyme (54,000 x g sediment): kinetics, activation by proteases, response to metals, stimulation by .V’-acetylglucosamine, and inhibition by polyoxin or UDP. One major difference was the much greater stability of the chitosomal chitin synthetase zymogen against spontaneous activation and destruction. Product (chitin microfibril) and enzyme (chitin synthetase) remained associated in a complex that was readily separated by centrifugation.