Requirement for omega and (omega-1)-hydroxylations of fatty acids by humancytochromes P450 2E1 and 4A11

Human liver microsomes and recombinant human P450 have been used as enzyme source in order to better understand the requirement for the optimal rate o f omega and (omega-1)-hydroxylations of fatty acids by cytochromes P450 2E1 and 4A, Three parameters were studied: alkyl chain length, presence and co nfiguration of double bond(s) in the alkyl chain, and involvement of carbox ylic function in the fatty acid binding inside the access channel of P450 a ctive site. The total rate of metabolite formation decreased when increasin g the allyl chain length of saturated fatty acids (from C12 to C16), while no hydroxylated metabolite was detected when liver microsomes were incubate d with stearic acid. However, unsaturated fatty acids, such as oleic, elaid ic and linoleic acids, were omega and (omega-1)-hydroxylated with an effici ency at least similar to palmitic acid. The (omega-1)/omega, ratio decrease d from 2.8 to 1 with lauric, myristic and palmitic acids as substrates, whi le the reverse was observed for unsaturated C18 fatty acids which are mainl y omega-hydroxylated, except for elaidic acid showing a metabolic profile q uite similar to those of saturated fatty acids. The double bond configurati on did not significantly modify the ability of hydroxylation of fatty acid, while the negatively charged carboxylic group allowed a configuration ener getically favourable for omega and (omega-1)-hydroxylation inside the acces s channel of active site.