Activity of long chain acyl-CoA synthetase in isolated alveolar type II cells

Immunocharacterization and developmental regulation of rabbit lung calcium-dependent phospholipid-binding proteins

The purpose of this work was to use the immunoblotting methods to study the 36 kDa calcium-dependent phospholipid-binding protein (PLBP) in the adult and fetal rabbit lungs to gain insight into the significance of this protein in lung development. The identity of the 36 kDa PLBP and the antigen specificity of the antiserum raised against this protein in the guinea pig were tested against known annexins and antibodies to the annexins. Our results showed that the rabbit lung 36 kDa PLBP contained only one protein which cross-reacted with antibodies against annexin 1. However, the 36 kDa PLBP was slightly smaller (36 vs. 37 kDa) and more acidic (pI 6.0 vs. 6.9) than the recombinant human annexin 1. The guinea pig antiserum only reacted with annexin 1, not with any of the other annexins tested. In the cytosolic fractions of the lung and the alveolar epithelial type II cells, and in the lung lavage fluid, the 36 kDa PLBP was by far the most prominent protein with minor presence of a 33 kDa protein recognized by the guinea pig antiserum. The amount of the 36 kDa PLBP of type II cells was 55% higher than that in the lung tissue and 2.6-times higher than that in the lung lavage (9.3 +/- 0.62, 6.0 +/- 0.31 and 3.6 +/- 0.04 micrograms/mg protein, respectively). The 36 kDa PLBP appeared in the fetal rabbit lungs as early as at 21 days gestation and increased 2-fold to reach the adult level at 27 days gestation (term 31 days). The high content of PLBP in type II cells and the rapid increase in this protein in the fetal lungs at late gestations suggest an important role of the 36 kDa PLBP in lung development and surfactant biogenesis.

Stereoselective arylpropionyl-CoA thioester formation in vitro

The inversion from R- to S-enantiomer that occurs for some arylpropionic acids may have both toxicological and therapeutic implications. To characterize some properties of this inversion, arylpropionyl-CoA thioester formation was studied in rat tissue homogenates and subcellular fractions for the enantiomers of fenoprofen, ibuprofen, and flurbiprofen. Thioesters were formed from (R)-fenoprofen (64%) and (R)-ibuprofen (33%) but not from the corresponding S-enantiomers or the enantiomers of flurbiprofen. This correlates with the extensive inversion of fenoprofen and ibuprofen and lack of inversion of flurbiprofen in vivo. Subcellular fractions from rat liver showed thioester formation to occur in mitochondria and microsomes but not cytosol. Once formed, the thioesters were readily racemized by whole rat liver homogenate, mitochondria, and cytosol, but only partially inverted (S:R = 0.3) in microsomes. Thioester formation from fenoprofen and ibuprofen was studied in tissue homogenate obtained from liver, diaphragm, kidney, lung, skeletal muscle, smooth muscle, fat, caecum, and intestines. The liver was at least 50-fold more efficient than the other tissues studied and would be expected to be a major organ of enantiomeric inversion. Our data support the hypothesis that R- to S-enantiomeric inversion of arylpropionic acids proceeds via the stereoselective formation of CoA thioesters followed by enzymatic racemization and hydrolysis of the thioesters to regenerate free acid.