LACK OF LECITHIN - RETINOL ACYLTRANSFERASE ACTIVITY IN CHICK LUNGS

Our previous study revealed that no retinyl esters were detectable in chick and hen lungs, suggesting that the retinol esterification system may be absent in these tissues. This possibility encouraged us to inv estigate whether chick lungs exhibit the activity of a retinol esterif ying enzyme, i.e., lecithin:retinol acyltransferase (LRAT). The LRAT a ctivity was assayed with dilauroyl phosphatidylcholine and either comp lex of retinol-cellular retinol-binding protein, type two or retinol-c ellular retinol-binding protein in microsomal preparations of lung, du odenum and liver of 7-day-old chicks. Relatively high levels of LRAT a ctivity were present in the duodenum and the liver of chicks as well a s in the rat lung. However, the chick lung exhibited no LRAT activity. The lungs of both rat and chick showed similar and low levels of acyl -CoA:retinol acyltransferase (ARAT) activity, but only rat lung, but n ot chick lung, contained a detectable amount of retinyl esters. Thus, the retinyl ester storage in the lung seems to depend on the presence of LRAT activity in the lung, but it is independent of the presence of ARAT activity in the lung. The absence of LRAT activity and retinyl e sters in the chick lung suggests that the retinol in the chick lung ma y not be provided from retinyl ester storage, and the retinol transfer red directly from serum should be utilized to generate retinoic acid.