[alginate](n) + GDP-alpha-D-mannuronate => [alginate](n+1) + GDP + H(+)
[alginate](n) + gdp-alpha-d-mannuronate => [alginate](n+1) + gdp + h(+)
[alginate](n) + GDP-alpha-D-mannuronate => [alginate](n+1) + GDP + H(+)
[alginate](n) + gdp-alpha-d-mannuronate => [alginate](n+1) + gdp + h(+)