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(Journal of Nutrition. 2001;131:1581-1583.)
© 2001 The American Society for Nutritional Sciences

Research Communication

Stability of Vitamin B-6–Dependent Aminotransferase Activity in Frozen Packed Erythrocytes Is Dependent on Storage Temperature1 ,2

Christine M. Hansen and Terry D. Shultz3

Department of Food Science and Human Nutrition, Washington State University, Pullman, WA 99164-6376

3To whom correspondence should be addressed. E-mail: shultz{at}wsu.edu.

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°C and under liquid nitrogen (-196°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°C samples, EALT basal activity decreased 17 and 22% (P <= 0.05 for both) by d 58 and 84, respectively, and EAST basal activity decreased 40% (P <= 0.05) by d 58. In -80 and -196°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°C for 7 to 84 d. Additionally, EAST-AC was significantly higher in -20 than -80 and -196°C samples on d 1 and 58, respectively. Erythrocytes may be frozen for 28 d at -20°C and 84 d at -80°C before analysis for EALT; for EAST, activity should be measured on fresh erythrocytes.

KEY WORDS: • erythrocyte alanine and aspartate aminotransferases • storage • stability • basal activity • activity coefficient






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