Phosphatidylcholine molecular species of calf lung surfactant.

This paper reports the detailed composition of molecular species of the phosphatidylcholines (PCs) in pulmonary surfactant from calves. PC isolated by thin-layer chromatography (TLC) was converted to benzoylated diradyl glyceride derivatives, which were separated by TLC according to linkage group. Quantification of linkage groups by analysis of total fatty acid content demonstrated that surfactant PC contained 97.2% diacyl, 2.4% alkyl-acyl, and 0.4% alkenyl-acyl compounds. The diacyl and alkyl-acyl diglyceride derivatives were separated into individual molecular species by high-performance liquid chromatography. Four major species constituted 87% of the diacyl compounds. Dipalmitoyl phosphatidylcholine (DPPC) was the most abundant constituent, contributing 41% of the total PC. A second disaturated species, palmitoyl-myristoyl phosphatidylcholine (PMPC), also contributed an additional 12% of total PC. At least 65% of PMPC occurred as the 1-palmitoyl-2-myristoyl/isomer, which has a lower melting point than the 1-myristoyl-2-palmitoyl compound. These results show that most of pulmonary surfactant PC is a relatively simple mixture, that numerous minor compounds are present in small but possibly important amounts, and that in surfactant from calves, the widely reported estimate that DPPC constitutes 60% of surfactant PC is too large by 50%.

Subcellular Localization of Oxygen Defense Enzymes in Soybean (Glycine max [L.] Merr.) Root Nodules.

Soybean (Glycine max [L.] Merr.) root nodules contain the enzymes of the ascorbate-glutathione pathway to minimize oxidative damage. In the present study, fractionation and immunocytochemistry were used to determine the subcellular location of the enzymes of this pathway. All four enzymes (ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase) were present in the soluble fraction from nodule plant cells and in isolated mitochondria. No activity was detected in peroxisomes. Bacteroids contained glutathione reductase but not the other enzymes of this pathway. Immunogold localization indicated that ascorbate peroxidase was present in the cytosol of infected and uninfected cells but not in the peribacteroid space. Results of immunogold and immunofluorescence studies indicated that monodehydroascorbate reductase was located primarily in the cell wall, suggesting that ascorbate regeneration in the cytoplasm may proceed primarily through the action of dehydroascorbate reductase. The possible roles of monodehydroascorbate reductase in cell wall metabolism are discussed.