Two forms of cytochrome P-450 (P-450I and P-450II) have been shown by several techniques to be present in both nonciliated bronchiolar cells (Clara) and alveolar type II cells isolated from rabbit lung. In contrast, the alveolar macrophage contains little or none of these cytochromes. Cross-reactivity between antibodies to cytochrome P-450I or P-450II and detergent-digested microsomes prepared from 80% type II or 70% Clara cell fractions was shown by Ouchterlony double immunodiffusion. The presence of both cytochromes was also demonstrated by histochemical immunofluorescence in smears of type II cells stained by a modified Papanicolaou procedure and Clara cells stained with nitroblue tetrazolium. However, this same fluorescent antibody technique used for localization of rabbit pulmonary cytochromes P-450I and P-450II in tissue sections showed most of the immunofluorescence in the Clara cells of the bronchiolar epithelium. SDS-polyacrylamide gel electrophoresis of microsomes from either the type II or Clara cell fractions produced bands which corresponded to cytochrome P-450I (52,000 daltons) and cytochrome P-450II (58,000 daltons).

Analyses of US prescription claims data between 2006 and 2015 for women 50 years of age or older showed declining use of oral estrogen generally and vaginally administered estrogen products specifically in age groups less than 65 years of age.

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We have obtained and studied a 105,000-g pellet from T-3-C1-2 cells, a cloned line of Friend virus-induced erythroleukemia cells. By difference spectrophotometry, the pellet was shown to contain cytochrome b5 and cytochrome P-450, In the present study, we have used the Friend virus-induced erythroleukemia T-3-C1-2 line as a model for early erythroid cells to study cytochrome b5 , a protein found in reticulocytes and mature erythrocytes . In non-nucleated erythroid cells, cytochrome b5 (16, 31) and cytochrome b5 reductase (16,20,30,39) exist in the cytoplasm as soluble molecules . Erythrocyte cytochrome 65 is similar to cytochrome b5 solubilized from microsomes of the liver. The amino acid composition of bovine erythrocyte cytochrome b5 I is in very good agreement with a segment (residues 1-97) of bovine liver microsomal cytochrome b5 (6) . Tryptic digestions It is our contention that, in the immature erythroid cell, cytochrome b5 is associated with membranes, and that sometime during the maturation process this hydrophobic membrane-bound protein is converted to a water-soluble molecule . In this paper we will present evidence that cytochrome b5 in an immature erythroid cell system exists as a membrane-bound protein. Some of these results have been presented previously in abstract form (36) .

The Netherlands. Reference should be made to BBA/DD/7.20/317A0/705 (1982) 228. The supplementary information includes: details of the preparation of lysosomes, microsomes, of a cathepsin fraction; and solub'flized liver microsomal cytochrome b s chromatography prof'fles, peptide maps and amino acid compositions of tryptic peptides from apocytochromes; expected tryptic peptides (structure and theoretical net charge).

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