Aliphatic molecules (C-6 to C-8) containing double or triple bonds as potential penicillin side-chain precursors

Three different hexenoyl-CoA derivatives (trans-2-hexenoyl-CoA, trans-3-hexenoyl-CoA and trans-trans-2,4-hexadienoyl-CoA), two octenoyl-CoA (trans-2-octenoyl-CoA, trans-3-octenoyl-CoA) and 2-octynoyl-CoA were tested as substrates of the enzyme acyl-CoA: 6-Aminopenicillanic acid acyltransferase (AT) from Penicillium chrysogenum. Only trans-3-hexenoyl-CoA and trans-3-octenoyl-CoA were recognized by AT and efficiently converted into penicillin F and octenoylpenicillin, respectively. The Km values for these substrates were 0.6 and 0.5 mM, suggesting that the affinity of AT for these molecules is similar to that reported for phenyl acetyl-CoA, octanoyl-CoA and hexanoyl-CoA (0.5, 0.6, and 1 mM, respectively). The absence of enzymatic activity shown by AT with the other acyl-CoA derivatives tested is due to the different position of the double or triple bond(s) in their aliphatic chains. The influence of the free rotation round the bond C-2-C-3 and possibility of planar conformation in such molecules and the importance in the formation of the enzyme-substrate complex is discussed.