The paradoxical effect of fatty acid on steroid-albumin interaction.

Careful investigation of the influence of palmitic and lauric acid on the interaction of progesterone and testosterone with several batches of untreated and defatted bovine and human serum albumins have revealed that, by contrast with published data for studies with progesterone as well as nonsteroid ligands, there is a surprising stimulation rather than inhibition of binding, albeit with a reduction of the apparent number of binding sites in almost all instances. Furthermore, fatty acid tends to minimize or eliminate the well-known differences in affinity between bovine and human albumin for interactions with these two steroids. The values for binding affinity in the interaction of testosterone with these batches of human serum albumin are significantly higher than those previously published by us and other authors and the value for progesterone-bovine albumin interaction is not in accordance with the "polarity rule". Studies of these same interactions by ultraviolet difference spectroscopy give further evidence of the augmentation in binding but, in the case of defatted bovine albumin only, the aromatic difference troughs are indicative of tyrosine perturbation whereas refatted bovine albumin, defatted and refatted human albumin manifest tryptophan perturbation. Quantitative correlation of perturbation with level of bound steroid suggests that fatty acid alters the ratio (possibly hydrogen-bonded to non hydrogen-bonded) of two forms of bound steroid. There is also further evidence that the binding sites for testosterone and progesterone are not identical.     

Alveolar type II cells: studies on the mode of release of lamellar bodies.

There is increasing evidence that type II alveolar cells are capable of synthesizing surface active material like that obtained from the airways. However a number of problems remain to be solved before it can be stated conclusively that type II cells synthesize the surface active material of the terminal airspace. Among these problems is that of secretion. A number of previous studies have given evidence of the release of lamellar bodies by merocrine secretion. In this study morphologic evidence is presented which supports the view that secretion of lamellar bodies is accomplished by exocytosis. At the apical surface of type II cells, sites can be found where the limiting membrane of the lamellar body is clearly fused with the type II cell plasma membrane and an open channel exists between the contents of the lamellar body and the alveolar space. At these sites the lamellar contents extrude into the airspace with consequent loss of the highly compact organization of intracellular lamellar bodies. The intactness and continuity of the membranes can be traced for the full extent of the exocytosis site. Freeze-etch replicas of the membranes of type II cells show depressions which may represent the sites of discharged lamellae. In addition, tongue-like folds are seen which could be explained as the extensions of cytoplasm which surround the releasing lamellar body and which may flap over the exocytosis pit after discharge. Micrographs of the alveolar space show disorganized lamellar whorls which appear to be unravelling to produce tubular myelin. In view of the unusually large size and lipid composition of lamellar bodies, a mechanism involving hydration of mucopolysaccharide contents as an aid to expulsion of lamellar contents is suggested.     

Stereoselective formation of benzo(c)phenanthrene (+)-(3S,4R) and (+)-(5S,6R)-oxides by cytochrome P450c in a highly purified and reconstituted system

The principal oxidative metabolites formed from benzo(c)phenanthrene (B(c)Ph) by the cytochromes P450 in liver microsomes from control and treated rats are the 3,4- and 5,6-arene oxides. A procedure is described which allows determination of the enantiomer composition and absolute configuration of these arene oxides based on HPLC separation of isomeric thiolate adducts formed with N-acetyl-L-cysteine in base. Incubation of [3H]-B(c)Ph with highly purified cytochrome P450c in a reconstituted monooxygenase system followed by trapping of the metabolically formed arene oxides as above indicated that the 3,4-oxide was predominantly the (+)-(3S,4R)-enantiomer (90%) and that the 5,6-oxide consisted mainly of the (+)-(5S,6R)-enantiomer (76%). The results are discussed in terms of their implications about the catalytic binding site of cytochrome P450c.