o-Toluoylcholine as substrate for measurement of serum pseudo-cholinesterase activity.

New synthetic substrates for serum pseudo-cholinesterase activity were compared with the common substrates for the routine assays, with regard to reactivity, specificity and stability; o- and m-toluoylcholine as well as o- and m-toluoyldimethylaminoethanol esters had selective specificities for pseudo-cholinesterase. The last three substrates, however, were unstable in solution at 4 degrees C. On the other hand, o-toluoylcholine could be stored in solution for several days with no appreciable degradation, and it was extremely stable with regard to pH and temperature. No or little hydrolysis of o-toluoylcholine was observed by various enzymes other than pseudo-cholinesterase. The enzymatic method using o-toluoylcholine as substrate was reproducible, and the results correlated well with those obtained using butylthiocholine as substrate and 5,5'-dithiobis-(2-nitrobenzoic acid) as color reagent. In conclusion, o-toluoylcholine is a favorable substrate for the determination of serum pseudo-cholinesterase activity.

Improved method for simultaneous determination of cholesterol in high- and low-density lipoproteins.

A previously described procedure for simultaneous determination of cholesterol in high- and low-density lipoproteins (HDL and LDL) [Clin. Chem. 24, 1504--1508 (1978)] has been improved by using centrifugation instead of ultrafiltration. Addition of NICl2 (2.0 mmol/L) to the reagent produced a good separation of HDL from the complex of low- and very-low-density lipoprotein-heparin-Ca2+ on centrifugation at 3000 rpm for 15 min. Replicate analyses for high-density lipoprotein cholesterol by the present method demonstrated the following intra-assay precision: mean = 389 mg/L, SD = 11 mg/L, CV = 2.8%. The present (y) and original (x) methods gave results that agreed reasonably well (n = 50, r = 0.960, y = 1.0x + 0.9). The enzymic method for HDL- or (HDL + LDL)-cholesterol after the separation of their fractions gave erroneous results, in particular in the cases of hyperbilirubinemic sera and in (HDL + LDL) fractions.