Effect of low lysine diet on rat protein metabolism

Prolonged lysine deficiency resulted in inhibition of growth of the rat and in lowered levels of albumin and beta-globulins, but not of total liver proteins. The apparent incorporation of [3H]lysine into total and chromosomal liver proteins, however, was increased in lysine deficient rats relative to pair-fed controls. The concentration of free lysine in neither serum nor liver was altered in lysine deficient rats. The specific radioactivity of liver free lysine 2 hours after administration of [3H]lysine was noticeably elevated in the deficient rats. However, when the pool of liver free lysine is considered, synthesis of all proteins studied was inhibited. The largest inhibitory effect was seen in serum albumin and total liver protein synthesis. Inhibition of snythesis of nuclear chromatin protein was less pronounced. The data indicate an adaptive mechanism operates to preserve liver lysine in rats fed lysine deficient diets for a prolonged period. In spite of retention of lysine, the synthesis of liver and serum proteins was inhibited.