sulfur metabolism hydrogen sulfide biosynthesis GO:0070814 KEGG:map00920 Conversion of sulfate to hydrogen sulfide, in preparation for incorporation into cysteine and methionine. Sulfate can provide sulfur for biosynthesis. The sulfur atom in sulfate is more oxidized than it is in cysteine and other organic molecules; thus sulfate must be reduced before it can be assimilated. This process is known as assimilatory sulfate reduction to distinguish it from the dissimilatory sulfate reduction that takes place when sulfate acts as an electron acceptor during anaerobic respiration. assimilatory sulfate reduction KEGG:map00230 PMID:15917234 PMID:10464198 KEGG:map01120 KEGG:map01100 UPa:UPA00140 sulfate activation pathway sulfate assimilation pathway pathway