title: Plasma cholinesterase phenotyping with use of visible-region spectrophotometry.
abstract: A method that overcomes the difficulties of the 240-nm benzoylcholine method for phenotyping plasma cholinesterases has been developed. After a timed reaction, under the same reaction conditions as in the classic procedure, choline is detected at 500 nm by use of choline oxidase coupled with the peroxidase/phenol/aminoantipyrine system. Cholinesterase activity measurements, calibrated by use of choline iodide as standard, are linearly related to results obtained with propionylthiocholine as substrate at 25 degrees C (y = 0.14x + 0.17, n = 30, r = 0.98). Results of differential inhibition with dibucaine and fluoride are virtually identical with those obtained by the ultraviolet method (y = 0.97x + 4.3, r = 0.995, and y = 0.93x - 0.5, r = 0.987, respectively) and give the same classification of homo- and heterozygotes for the usual, atypical, and fluoride-resistant variants. The new method has substantial advantages in that it eliminates the difficulties associated with measuring small changes in high absorbances at a suboptimal wavelength on a steep portion of the absorption curve.
mesh_terms: D000429:Alcohol Oxidoreductases; D002794:Choline / Q000032:analysis; D002802:Cholinesterases / Q000097:blood / Q000235:genetics*; D003992:Dibucaine; D005459:Fluorides; D006801:Humans; D010641:Phenotype; D013053:Spectrophotometry / Q000379:methods; D013379:Substrate Specificity
chemical_list: D000429:Alcohol Oxidoreductases; C019888:choline oxidase; D002802:Cholinesterases; D003992:Dibucaine; D002794:Choline; D005459:Fluorides