Amount and quality of dietary protein regulate lecithin:retinol acyltransferase activity without change in cellular retinol-binding protein, type two in rat jejunum

Abstract

The effects of amount and quality of dietary protein on the cellular retinol-binding protein (type two) and two enzymes for retinol esterification, i.e., lecithin:retinol acyltransferase and acyl-CoA:retinol acyltransferase in rat jejunum were examined. Three groups of five rats were pair-fed defined diets for 14 days. The control group was fed a diet containing 20% casein; the two experimental groups received diets containing 5% casein or 20% gluten. Feeding the 5% casein diet or the 20% gluten diet decreased serum concentration of retinol and retinol-binding protein and increased liver total retinol and retinol-binding protein contents. The lecithin:retinol acyltransferase activity in jejunal microsomes, which was determined using retinol bound to cellular retinol-binding protein (type two), was significantly reduced in animals fed the 20% gluten diet (by 30%) as compared with animals fed the 20% casein diet. Feeding the 5% casein diet also led to a slight decrease in the segmental lecithin:retinol acyltransferase activity. The acyl-CoA:retinol acyltransferase activity was unaffected by feeding these diets. The jejunal cytosolic cellular retinol-binding protein (type two) content was also unchanged by feeding these diets. Feeding the 20% wheat gluten diet resulted in remarkable low levels of the unesterified retinol (by 64%), retinyl palmitate (by 32%), and protein (by 47%) in the whole jejunal mucosa, when compared with the corresponding values of the 20% casein group. These results suggest that the dietary protein malnutrition will suppress intestinal esterification of retinol absorbed by a decline of lecithin:retinol acyltransferase activity and without change in intestinal cellular retinol-binding protein (type two) level. The results also suggest that retinol uptake may decrease due to an impaired absorption process in protein malnutritional status.