FIG 1.

3-Hydroxypropionate/4-hydroxybutyrate cycle in M. sedula and N. maritimus (adapted from reference 13). The reactions controlling energy efficiency of the cycle in M. sedula are shown in green, and those for N. maritimus variant are shown in red. The common reactions for both are shown in black. Enzymes: 1, acetyl-CoA carboxylase; 2, malonyl-CoA reductase; 3, malonic semialdehyde reductase; 4, 3-hydroxypropionyl-CoA synthetase; 5, 3-hydroxypropionyl-CoA dehydratase; 6, acryloyl-CoA reductase; 7, propionyl-CoA carboxylase; 8, methylmalonyl-CoA epimerase; 9, methylmalonyl-CoA isomerase; 10, succinyl-CoA reductase; 11, succinic semialdehyde reductase; 12, 4-hydroxybutyryl-CoA synthetase; 13, 4-hydroxybutyryl-CoA dehydratase; 14, crotonyl-CoA hydratase; 15, (S)-3-hydroxybutyryl-CoA dehydrogenase; 16, acetoacetyl-CoA β-ketothiolase.