[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(+) => [alginate](n) + gdp-alpha-d-mannuronate