APS and PAPS are intermediates in the reduction of sulfate to sulfite, an exothermic conversion that is carried out by sulfate-reducing bacteria.
ˌeɪpˌiːˈɛs ænd pˈæps ɑːɹ ˌɪntɚmˈiːdiəts ɪnðə ɹᵻdˈʌkʃən ʌv sˈʌlfeɪt tə sˈʌlfaɪt, ɐn ɛɡzəðˈɜːmɪk kənvˈɜːʒən ðæt ɪz kˈæɹid ˈaʊt baɪ sˈʌlfeɪtɹᵻdˈuːsɪŋ bæktˈɪɹiə.