Metabolic transit of lysinoalanine (LAL) bound to protein and of free radioactive [14C]-lysinoalanine.

Abstract

Three alkali-treated proteins (lactalbumin, fish protein isolate and soya isolate) containing respectively 1.79, 0.38 and 0.12 g of lysinoalanine (LAL)/16 g N, were submitted to an “in vitro” enzymatic hydrolysis (pepsin then pancreatin); the higher the level of LAL present in the proteins the smaller was the proportion of LAL liberated in the dialysable fractions of the enzymatic hydrolysates. These same alkali-treated proteins were also given to rats in feeding studies. The faecal LAL varied between 30 and 50% of the ingested quantity, and the urinary LAL between 10 and 25%. The total recovery was always inferior to 100% showing that a certain proportion of LAL was modified in the organism. In the urine, LAL was partially present as free LAL and also as combined LAL, its recovery being higher after acid hydrolysis. The experiments performed with radioactive LAL confirmed the above-mentioned results and gave complementary data: LAL was partially transformed into 14CO2; the urine contained free LAL and several metabolites, some combined LAL, probably acetyl derivatives, and some products of catabolism. The proportions of the urinary products varied widely from one animal to another. The kidneys play an important role in the chemical modification (acetylation) of LAL and in the filtration of the excretion products which is most efficient for the most acetylated catabolites of LAL. Although there is practically no difference in the pattern of the urinary catabolites in the rodents (Sprague-Dawley rat, Swiss mouse, Syrian hamster), the rat kidney retains LAL and its catabolites at levels much higher than the kidneys of other species; this retention is localized in the inner part of the cortex.