title: Stability of vitamin B-6-dependent aminotransferase activity in frozen packed erythrocytes is dependent on storage temperature.
abstract: Pyridoxal 5'-phosphate (PLP) stimulation of erythrocyte alanine and aspartate aminotransferase (EALT, EAST) activities is a frequently used functional measure of vitamin B-6 status. Stability of enzyme activities and activity coefficients (AC, stimulated / unstimulated) was assessed in packed erythrocytes frozen at -20, -80 degrees C and under liquid nitrogen (-196 degrees C). Activities of EALT and EAST, with and without added PLP, were determined in fresh erythrocytes (d 0) and frozen samples on d 1, 7, 14, 28, 58 and 84. In -20 degrees C samples, EALT basal activity decreased 17 and 22% (P < or = 0.05 for both) by d 58 and 84, respectively, and EAST basal activity decreased 40% (P < or = 0.05) by d 58. In -80 and -196 degrees C samples, EALT and EAST basal activities did not change significantly. Activity coefficients did not differ significantly from d 0 at any storage temperature, but EAST-AC increased 9-19% (nonsignificant) in samples stored at -20 and -80 degrees C for 7 to 84 d. Additionally, EAST-AC was significantly higher in -20 than -80 and -196 degrees C samples on d 1 and 58, respectively. Erythrocytes may be frozen for 28 d at -20 degrees C and 84 d at -80 degrees C before analysis for EALT; for EAST, activity should be measured on fresh erythrocytes.
authors.affiliation: Department of Food Science and Human Nutrition, Washington State University, Pullman, WA 99164-6376, USA.
authors.forename: C M
authors.initials: CM
authors.lastname: Hansen
authors.forename: T D
authors.initials: TD
authors.lastname: Shultz
mesh_terms: D000328:Adult; D000410:Alanine Transaminase / Q000097:blood* / Q000187:drug effects; D001219:Aspartate Aminotransferases / Q000097:blood* / Q000187:drug effects; D015925:Cryopreservation; D004355:Drug Stability; D004356:Drug Storage; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011736:Pyridoxine / Q000494:pharmacology*
chemical_list: D001219:Aspartate Aminotransferases; D000410:Alanine Transaminase; D011736:Pyridoxine