This paper is the fourth in a series dealing with reference procedures for the measurement of catalytic activity concentrations of enzymes at 37 degrees C and the certification of reference preparations. Other parts deal with: Part 1. The Concept of Reference Procedures for the Measurement of Catalytic Activity Concentrations of Enzymes; Part 2. Reference Procedure for the Measurement of Catalytic Concentration of Creatine Kinase; Part 3. Reference Procedure for the Measurement of Catalytic Concentration of Lactate Dehydrogenase; Part 5. Reference Procedure for the Measurement of Catalytic Concentration of Aspartate Aminotransferase; Part 6. Reference Procedure for the Measurement of Catalytic Concentration of Gamma-Glutamyltransferase; Part 7. Certification of Four Reference Materials for the Determination of Enzymatic Activity of Gamma-Glutamyltransferase, Lactate Dehydrogenase, Alanine Aminotransferase and Creatine Kinase at 37 degrees C. A document describing the determination of preliminary upper reference limits is also in preparation. The procedure described here is deduced from the previously described 30 degrees C IFCC reference method. Differences are tabulated and commented on in Appendix 2.

This paper is the sixth in a series dealing with reference procedures for the measurement of catalytic activity concentrations of enzymes at 37 degrees C and the certification of reference preparations. Other parts deal with: Part 1. The Concept of Reference Procedures for the Measurement of Catalytic Activity Concentrations of Enzymes; Part 2. Reference Procedure for the Measurement of Catalytic Concentration of Creatine Kinase; Part 3. Reference Procedure for the Measurement of Catalytic Concentration of Lactate Dehydrogenase; Part 4. Reference Procedure for the Measurement of Catalytic Concentration of Alanine Aminotransferase; Part 5. Reference Procedure for the Measurement of Catalytic Concentration of Aspartate Aminotransferase; Part 7. Certification of Four Reference Materials for the Determination of Enzymatic Activity of Gamma-Glutamyltransferase, Lactate Dehydrogenase, Alanine Aminotransferase and Creatine Kinase at 37 degrees C A document describing the determination of preliminary upper reference limits is also in preparation. The procedure described here is deduced from the previously described 30 degrees C IFCC reference method. Differences are tabulated and commented on in Appendix 1.

This paper is the third in a series dealing with reference procedures for the measurement of catalytic activity concentrations of enzymes at 37 degrees C and the certification of reference preparations. Other parts deal with: Part 1. The Concept of Reference Procedures for the Measurement of Catalytic Activity Concentrations of Enzymes; Part 2. Reference Procedure for the Measurement of Catalytic Concentration of Creatine Kinase; Part 4. Reference Procedure for the Measurement of Catalytic Concentration of Alanine Aminotransferase; Part 5. Reference Procedure for the Measurement of Catalytic Concentration of Aspartate Aminotransferase; Part 6. Reference Procedure for the Measurement of Catalytic Concentration of gamma-Glutamyltransferase; Part 7. Certification of Four Reference Materials tamyltransferase, Lactate Dehydrogenase, Alanine Aminotransferase and Creatine Kinase at 37 degrees C. A document describing the determination of preliminary upper reference limits is also in preparation. The procedure described here is deduced from the previously described 30 degrees C IFCC reference method (1). Differences are tabulated and commented on in Appendix 1.

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.

We describe a new electrochemical method for the determination of erythrocyte acetylcholinesterase activity (EC 3.1.1.7) and plasma cholinesterase (EC 3.1.1.8) activity, based on the measurements of pH variation due to release of acetic acid from acetylcholine. The major advantages of the differential pH procedure are simplicity, high reproducibility, no need for pre-treatment of samples, automatic correction of sample blanks, and speed and direct measurement of enzymatic reaction. The proposed methods are linear up to 7400 U/L at 30°C and correlate well with the manual spectrophotometric method of Ellman1 for plasma cholinesterase and for washed erythrocytes. We adapted the same technique for the determination of erythrocyte cholinesterase using whole blood as sample and quinidine sulphate as inhibitor of pseudocholinesterase.