Eric Dubreucq

Substrate specificity of the lipase fromCandida parapsilosis

Substrate specificity of the acyltransferase activity of the lipase (EC 3.1.1.3) fromCandida parapsilosis CBS 604 was studied in aqueous media. The specificity toward both acid and alcohol parts of a large number of acylglycerols and aliphatic esters was investigated. This lipase showed a high activity in the presence of esters with long-chain fatty acids and particularly unsaturated fatty acids with acis-Δ9 double bond. It was observed that the activity profile depended not only on the alcohol part of the acyl ester, but also on the temperature of the reactant medium. The best lipid substrates had their melting point between −40 to +20°C, 14 to 18 carbon atoms in the acyl group and 1 to 4 carbon atoms in the alkyl group. The enzyme, defined as an acyltransferase in a previous paper, showed a high affinity for primary and secondary alcohols with a short carbon chain (1 to 5 carbon atoms) as acyl acceptors. The influence of free alcohols in the reactant medium on the hydrolysis and alcoholysis activities of the enzyme is discussed. Two phenomena seem to be involved, depending on the alcohol: competition with water for the acyltransfer reaction and lipid substrate dilution when the alcohol places at the oil/water interface.

Monohydroxamic acid biosynthesis

Abstract Hydroxamic acids (HA), with the general formula R–CO–NHOH, are chelating agents which may be used in a number of interesting applications, such as medicine and waste water treatment. In this paper, we describe the enzymatic synthesis of HA with various chain lengths (from C2 to C18), using three microbial enzymes. For short- and middle-chain HA synthesis, using amidases from Rhodococcus sp. R312, the optimal working pH was found to be pH 7 or 8, depending on the amide substrate used. Different Michaelis–Menten constants were also determined. For fatty HA synthesis, using lipase from Candida parapsilosis, the optimal working conditions were determined to be pH 6, 1 M hydroxylamine and 40°C. Because of the favorable bioconversion yields achieved, the enzymatic synthesis of HA with the appropriate biocatalysts appears to be an interesting alternative to chemical synthesis.

Study of the Δ12-desaturase system ofLipomyces starkeyi

The specific activity of the microsomal Δ12-desaturase system, which transforms oleic acid into linoleic acid, was about 16 pmol/min/mg protein. However, most of the total activity was nonsedimentable even after a 200000×g centrifugation for 100 min. The study of various physicochemical parameters showed that this enzymatic complex, functioning optimally between pH 7 and 8, had low thermal stability. Ca2+, which may cause an aggregation of the microsomes, and Hg2+ completely inhibited the activity, whereas Mg2+, Mn2+, and Zn2+ were activators. The Δ12-desaturase system was relatively specific toward oleic acid, though isomers of this fatty acid also had an action, either as substrates or as competitive inhibitors, on the activity of the system. The study of the effect of the exogenous oleoyl-CoA and elaidoyl-CoA on the specific activity of the Δ12-desaturase system showed a preference toward oleoyl-CoA.