a series of amp analogs in which a terminal carboxylate residue , linked to c 4 ' of the ribose moiety of adenosine by zero , one , or two methylene groups ( 1,2,3 ) or by the unsaturated ethylidene link ( 4 ) replaces the phosphate anion , is tested for activity as substrates or effectors of three enzymes known to interact with amp with a different degree of specificity .
C0031603
phosphate
C0003075
anion