A synthetic approach for the preparation of amlnoacyl, amlnopeptyl, or amlnodepslpeptyl steroldal esters Is descrlbed.

Following the selection of the most appropriate method for emulsification and the optimization of the reaction medium, interlaboratory studies were conducted to check the effect of preparing Substrates and measuring the catalytic concentration of lipase at different sites äs well äs the effect of transport on emulsion. The determinations of lipase activity in an abnormal chemistry control against emulsions prepared by two laboratories (and used by both laboratories) and, also, against five separate emulsions prepared by one laboratory (and used by five different laboratories) resulted in average enzyme activity vahies (2234 ±125 and 2263 ± 204 U/l respectively) which are not statistically different. Standard preparations of lipase, control sera and reference materials can therefore be titrated according to the procedure followed by at least two laboratories for at least 3 days against two separate emulsions. Introduction(6-11). Differences between the assay procedures hitherto described are related to < he c ™P ositi ™ of the reacFor decades, the unique properties of pancreatic lipase (EC 3.1.1.3) have sustained a controversy over the tlon mixture ^& ^P e ™ d ^ncentration of bile salt) method and the in vitro conditions for reliable.determin-and the *W* of emulsification procedure employed. Owations of the enzyme catalytic concentration (l -4). The in § to * e multitude of emulsification devices, there is a most widely used routine indkect turbidimetric method g^at Variation in the physical state of Substrates, which (5) requires the prior direct assay of Standards and, in turn affects the expression of lipase activity, thus hinmoreover, is restricted to low Substrate concentrations, dering the comparability of results obtained by difowing to the limitations of spectrophotometry (2, 4). The ferent laboratories. latest titrimetric assays, which make use of continuousmonitoring pH-stat techniques for direct titration of the Within the context of this work, an effort was made to released fatty acids, offer a satisfactory approach to the deal with some of the main factors involved in the prepproblern, because they allow the use of high Substrate aration of Substrates and to subject the whole titrimetric concentrations while photometric artefacts are excluded procedure to an interlaboratory study.

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There is a lack of certified reference material (CRM) for lipase catalytic activity. Consequently between-method comparability is very poor. The aim of this study was to produce two lipase CRMs, one from human pancreatic juice (BCR 693), and another using recombinant technologies (BCR 694). Lipase was purified from pancreatic juice, using column chromatography and isoelectric focusing. Recombinant lipase was produced with a transfected cell line and purified with column chromatography. Adding buffered bovine serum albumin and subsequent freeze-drying were used to stabilize both materials. A standardized titrimetric method was employed to compare their catalytic properties to those of two plasma pools of patients suffering from acute pancreatitis. About 5 kU (titrimetry, 37 degrees C) of each material were obtained. They were lyophilized without apparent modifications of their catalytic properties, which stayed identical to those exhibited by the enzyme present in patient's pools. Stability of both materials was estimated at several years when stored in a dry form at -20 degrees C. Both materials appear to have similar catalytic properties and stability and were found commutable as regards a reference method and a routine measurement procedure. An international certification campaign will be carried out to assign values to BCR 693 and BCR 694.

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