label: [(1->4)-beta-D-mannuronosyl](n) + GDP-alpha-D-mannuronate = [(1->4)-beta-D-mannuronosyl](n+1) + GDP + H(+)
label_lc: [(1->4)-beta-d-mannuronosyl](n) + gdp-alpha-d-mannuronate = [(1->4)-beta-d-mannuronosyl](n+1) + gdp + h(+)