Aspartate aminotransferase activity in experimentally induced asymptomatic vitamin B6 deficiency in chicks
1991
Masse, P.G. | Vuilleumier, J.P. | Weiser, H.
Forty-five male Lohmann chicks were grown up to 6 weeks of age. The experimental diet containing a high protein level (30%) was aimed at increasing the metabolic need for PN. Microbiological analysis on the basal ration revealed a marginal content of 4.7 micromole PN/kg. The vitamin B6 status was assessed at the end of the experiment according to the basal activity of aspartate aminotransferase (AspAT) in plasma and in erythrocytes, and the in vitro stimulated activity with pyridoxal 5'-phosphate (PLP). None of the deficient chicks had any clinical signs attributable to malfunction of the nervous system, and they grew as well as those receiving the control diet. Vitamin B6 deficiency was biochemically confirmed by a significant depression of AspAT activity in plasma (p < 0.001) and in erythrocytes (p < 0.01). The addition of PLP in vitro enhanced the catalytic activity of the plasma enzyme, but had negligible effect on the erythrocyte enzyme. The degree of stimulation in vitro of the apoenzyme of AspAT not only depends on the endogenous vitamin B6 content, but also on the basal activity of the enzyme. A 15-day repletion period with a daily oral dose (50 micromole PN) did not result in a complete restoration of the enzyme activity, indicating that the availability of apoenzyme had been curtailed. This experiment demonstrated that chicks fed a high protein corn-soyamin diet with a limited amount of PN but containing Saccharomyces yeast showed no nervous signs or perosis, but significant metabolic disturbances. The study was aimed at simulating an early stage (asymptomatic) of pyridoxine deficiency, as found in humans afflicted by a physiological or metabolic stress condition such as pregnancy or alcoholism.
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