[3-O-methyl-alpha-D-mannosyl-(1->4)](n)-3-O-methyl-D-mannose + GDP-alpha-D-mannose <=> alpha-D-mannosyl-(1->4)-[3-O-methyl-alpha-D-mannosyl-(1->4)](n)-3-O-methyl-D-mannose + GDP + H(+)
[3-o-methyl-alpha-d-mannosyl-(1->4)](n)-3-o-methyl-d-mannose + gdp-alpha-d-mannose <=> alpha-d-mannosyl-(1->4)-[3-o-methyl-alpha-d-mannosyl-(1->4)](n)-3-o-methyl-d-mannose + gdp + h(+)
[3-O-methyl-alpha-D-mannosyl-(1->4)](n)-3-O-methyl-D-mannose + GDP-alpha-D-mannose <=> alpha-D-mannosyl-(1->4)-[3-O-methyl-alpha-D-mannosyl-(1->4)](n)-3-O-methyl-D-mannose + GDP + H(+)
[3-o-methyl-alpha-d-mannosyl-(1->4)](n)-3-o-methyl-d-mannose + gdp-alpha-d-mannose <=> alpha-d-mannosyl-(1->4)-[3-o-methyl-alpha-d-mannosyl-(1->4)](n)-3-o-methyl-d-mannose + gdp + h(+)