The effect of vitamin B6 deficiency on the desaturation of linoleic acid (18:2n-6) to γ-linolenic acid (18:3n-6) in rat liver microsomes was studied. Rats fed with a vitamin B6-deficient 70% casein diet for 5 weeks displayed a striking decrease mainly in the activity of terminal Δ6-desaturase in the 18:2n-6 desaturation system, although the activity of the electron-transport enzyme, NADH-cytochrome b5 reductase, was also significantly decreased. The 18:2n-6 desaturation index, the arachidonic acid (20:4n-6)/ 18:2n-6 ratio in the liver microsomal total lipids and in their phosphatidylcholine (PC) fraction, decreased together with the microsomal Δ6-desaturase activity, these changes being quite faithfully reflected in the plasma lipid. Among the microsomal lipid components, the PC content significantly decreased. In addition, a highly positive correlation was found between the PC content and Δ6-desaturase activity in liver microsomes. In an in vitro experiment, the Δ6-desaturase activity decreased linearly with increasing rate of PC hydrolysis by phospholipase C. These results suggest that the altered PC content in microsomes induced by vitamin B6 deficiency in vivo may affect the 18:2n-6 desaturation and thus decrease the biosynthesis of 20:4n-6
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She et al. (1994) studied this question.
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