Reaction solutions are disclosed herein comprising water, sucrose and a glucosyltransferase enzyme that synthesizes poly alpha-1,3-glucan. The glucosyltransferase enzyme can synthesize insoluble glucan polymer having at least 50% alpha-1,3 glycosidic linkages and a number average degree of polymerization of at least 100. Further disclosed are methods of using such glucosyltransferase enzymes to produce insoluble poly alpha-1,3-glucan.