Determination of Choline, Phosphorylcholine, and Betaine

This chapter describes the determination of choline, phosphorylcholine, and betaine. Two methods exist for the analysis of choline in plasma. First method utilizes the formation of choline periodide, a colored complex measurable in 1,2-dichloroethane and permits the estimation of as little as 5 μg of choline. A radioisotopic method has also proved to be quite simple and sensitive for the analysis of plasma choline. Measurement of phosphorylcholine in tissue extracts is accomplished by taking advantage of an earlier findings that acid phosphatase can specifically liberate choline from phosphorylcholine. After the measurement of choline in the phosphatase-treated extract, phosphorylcholine can be determined by taking the difference between the choline levels in the phosphatase-treated and non-treated extracts. In the assay for betaine, betaine periodide is completely precipitated between pH 0 and 1. In the procedure for the determination of choline in the phosphatase-treated extract to arrive at the estimation of phosphorylcholine, it was found that acid phosphatase of wheat germ was not effective, but the acid phosphatase from a potato source afforded the complete hydrolysis of phosphorylcholine at pH 4.8.