Inhibition of lysyl hydroxylase and prolyl 3-hydroxylase was studied with 23 selected aromatic and aliphatic structural analogues of 2-oxoglutarate and the results were compared with those previously reported for prolyl 4-hydroxylase. All the compounds inhibited the hydroxylases competitively with respect to 2-oxoglutarate and noncompetitively with respect to Fe2+ and the peptide substrate. The inhibition patterns for the three collagen hydroxylases were basically similar, but certain differences in detail emerged. One systematic difference was that lysyl hydroxylase had a higher Ki for almost all the compounds than had the two prolyl hydroxylases. Another interesting difference was that pyridine-2,4-dicarboxylate was the most potent inhibitor of lysyl hydroxylase and prolyl 3-hydroxylase, with Ki values of 50 microM and 3 microM respectively, whereas pyridine-2,5-dicarboxylate was the most potent inhibitor of prolyl 4-hydroxylase. These and other data suggest that the three collagen hydroxylases have similar but not identical 2-oxoglutarate-binding sites. Pyridine-2,4-dicarboxylate and pyridine-2,5-dicarboxylate and their corresponding benzene derivatives were also found to inhibit 2-oxoglutarate dehydrogenase, but with this enzyme, unlike the collagen hydroxylases, no distinct difference in the Ki values was found between the corresponding pyridine and benzene derivatives. This demonstrates the importance of the metal ion for the binding of various compounds at the 2-oxoglutarate-binding site of the collagen hydroxylases. 2-Oxoadipate was shown to replace 2-oxoglutarate in the lysyl hydroxylase and 2-oxoglutarate dehydrogenase reactions, as has previously been reported for prolyl 4-hydroxylase, whereas no other 2-oxo acid tested had any co-substrate activity. The 2-oxoglutarate-binding site of these enzymes is thus flexible to a certain degree, as it can accommodate molecules of different shapes and volumes. On the basis of the present data pyridine-2,5-dicarboxylate seems to be a quite specific inhibitor of prolyl 4-hydroxylase, the Ki for 2-oxoglutarate dehydrogenase being about 4000-fold higher.