Calcium is required for the reduction of sulfite from hydrogen in a reconstituted electron transfer chain from the sulfate reducing bacterium, Desulfovibrio gigas.

Calcium is found a strong stimulator of sulfite reduction from hydrogen. A coupling protein of molecular weight 65,000 can be isolated from Desulfovibrio gigas. It functions in a reconstituted electron transfer chain between hydrogenase and sulfite reductase. Its N-terminal sequence shows high homologies with calcium or magnesium binding sites from other calcium-binding proteins.