Thiol S-methyltransferase that catalyzes the transfer of a methyl group from S-adenosyl-l-methionine to hydrogen sulfide and other thiol compounds including dithiothreitol, 7alpha-thiospironolactone, L-penicillamine, and captopril. a thiol + S-adenosyl-L-methionine = a methyl thioether + H(+) + S-adenosyl-L-homocysteine Highly concentrated in the perinuclear area of the endoplasmic reticulum (ER) and surrounding lipid droplets. May be associated with the specific regions of the LR that form lipid droplets and targeted to the initial deposits of lipids where the lipid droplets form. Belongs to the methyltransferase superfamily.