Effect of Vitamin B₆ Deficiency on Linoleic Acid Desaturation in the Arachidonic Acid Biosynthesis of Rat Liver Microsomes

Abstract

The effect of vitamin B₆ deticiency 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 5weeks displayed a striking decrease mainly in the activity of terminal darutaΔ6-desaturase in the 18 : 2n-6desaturation 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 A6-desaturase activity, these changes being quite faithfully reflected in the plasma lipid. Among the microsomal lipid components, the PC content signiticantly 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 deticiency in vivo may affect the 18 : 2n-6 desaturation and thus decrease the biosynthesis of 20 : 4n-6.