preferred_name: alpha-D-mannosyl-(1->4)-[3-O-methyl-alpha-D-mannosyl-(1->4)](n)-1-O,3-O-dimethyl-alpha-D-mannose + GDP + H(+) => [3-O-methyl-alpha-D-mannosyl-(1->4)](n)-1-O,3-O-dimethyl-alpha-D-mannose + GDP-alpha-D-mannose