QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Purchase Article View Shopping Cart Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Lumeng, L. Articles by Oei, T. O. Search for Related Content PubMed PubMed Citation Articles by Lumeng, L. Articles by Oei, T. O.

Comparison of the Use of L-Tyrosine Apodecarboxylase and D-Serine Apodehydratase for Plasma Pyridoxal Phosphate Assay

Department of Medicine, Biochemistry ^* Department of Pathology, Indiana University School of Medicine and the Richard L. Roudebush Veterans Administration Medical Center, Indianapolis, IN 46223

The enzymatic methods for plasma pyridoxal 5'-phosphate (PLP) assay using L-tyrosine apodecarboxylase (apo-LTD) and D-serine apodehydratase (apo-DSD) were compared with respect to their operating characteristics, accuracy and precision. With the apo-LTD assay, the recovery of authentic PLP added to irradiated plasma was 96–100% and the precision for within-run and run-to-run replicates was 4–5% (coefficient of variation). The recovery of authentic PLP with the apo-DSD assay tended to be lower (viz., 95%) and the within-run and run-to-run coefficients of variation tended to be higher (viz., 5–6%), but these differences were not statistically significant. When these two assay methods were directly compared in determining the plasma PLP levels of 67 hospitalized patients, the regression lines exhibited correlation coefficients of 0.89 and 0.92 and slopes of 0.77 and 0.78, respectively. When the plasma PLP values were less than 7.5 ng/ml, the values determined by the apo-DSD assay tended to be higher than those measured by the apo-LTD method and vice versa. The lack of better agreement between the two assay methods may be explained by the fact that an inhibitor exists in plasma extracts that impairs the binding of PLP to apo-DSD and that the correction for this interference may not be uniform from one plasma sample to another. However, if one is willing to tolerate the small discrepancies between the values obtained by the apo-DSD and apo-LTD assays, these assay methods can be used interchangeably. The apo-DSD assay has the advantage of being easily adapted to a modern automated spectrophotometric centrifugal analyzer.

KEY WORDS: • vitamin B-6 • pyridoxal phosphate • enzymatic assay • D-serine dehydratase apoenzyme • L-tyrosine decarboxylase apoenzyme • plasma pyridoxal phosphate

Manuscript received 8 August 1983.