Figure 4 Chemical structures of several substrates of recombinant Pc Aad1p. Chemical structure of some of the aldehyde and alcohol substrates of Pc

Aad1p analyzed in this study ordered by chemical function and substitution: aliphatic aldehydes (n-Hexanal), aryl-aldehydes (Benzaldehyde and related compounds, 2-Phenylacetaldehyde and trans-Cinnamaldehyde) and aryl-alcohols. Other substrates are presented in Table 1 and 2. Among the substrates assayed for the oxidation reaction by Pc Aad1p with NADP+ as cofactor, the highest activity was by far that on Veratryl alcohol (3,4-Dimethoxybenzyl alcohol), whereas other mono-, di- or tri-substituted methoxybenzyl alcohols showed poor reactivity with this enzyme. Interestingly, the Pc Aad1p showed PLX3397 research buy 46% activity on 4-Hydroxy-3-Methoxybenzyl alcohol Ipilimumab in vitro (Vanillyl alcohol) as compared

to that on Veratryl alcohol. No activity could be detected on many other linear aliphatic, ramified aliphatic or aryl alcohol substrates as well as on some acetate esterified aryl and ramified alcohols. Altogether, these results suggest that a specific size, structure and conformation of the substrate are necessary to allow concurrent interactions of the carbonyl group

of the substrate molecule with the cofactor and with key amino acids of the active site. Other parameters like the relative hydrophilic/hydrophobic character of the substrates and of the active site as well as the possibility of resonance delocalization within a conjugated π system of the substrate might also account for relative specificity of the Aad1p enzyme to its substrate. We then obtained precise kinetic parameters of Pc Aad1p with respect to cofactor dependency and affinity to several substrates like Veratraldehyde or Veratryl alcohol (Table 2). In the reductive sense, using 0.2 mM Veratraldehyde, the activity of Pc Aad1p for NADPH oxidation followed O-methylated flavonoid a Michaelis-Menten curve with an apparent K M  = 39 μM. NADH could also be used as electron donor though exhibiting a lower affinity (K M  = 220 μM). The enzyme was only active with NADP+ in the oxidation sense of the reaction, with a K M of 38 μM. Moreover, the activity of this enzyme determined against Veratraldehyde or Veratryl alcohol using NADPH or NADP+ as cofactor showed a slight inhibition at elevated concentration of substrate (Figure 5). However, the apparent K M for Veratraldehyde was 30-fold that for Veratryl alcohol.