Regulation of apo-A-I processing in cultured hepatocytes

Apo-A-I, the major protein component of high density lipoproteins, appears intracellularly as an intermediate precursor (pro-apo-A-I) with a hexapeptide extension (RHFWQQ) at its amino terminus. Proteolytic processing of pro-apo-A-I to apo-A-I has been shown to occur extracellularly in cell and organ cultures from rat and human tissues. Recently, however, intracellular conversion has been detected in chickens. To determine what distinguishes and regulates these two processing methods, the proteolytic processing and secretion of apo-A-I was studied by metabolic labeling in chick hepatocytes and in Hep-G2 cells (derived from a human hepatocellular carcinoma). The proportions of intracellular and secreted pro-apo-A-I and apo-A-I were measured by sequencing NH2-terminal portions of the proteins and determining the location of radio-labeled amino acids. Chick hepatocytes cultured in the absence of hormones or fetal bovine serum secreted primarily processed apo-A-I (83%). In the presence of serum these cells secreted only pro-apo-A-I, whereas incubation with a combination of hormones (insulin, triiodothyronine, dexamethasone) resulted in secretion of a nearly equal mixture of the pro- and processed forms of the protein. In contrast, Hep-G2 cells, maintained in the absence of serum, secreted only pro-apo-A-I; when grown in the presence of serum these cells secreted a mixture of pro- and processed apo-A-I. Under conditions in which chick hepatocytes and Hep-G2 cells secreted both forms of the protein, a mixture of pro- and processed apo-A-I was also found intracellularly; when only the pro-form was secreted, the cells likewise contained only pro-apo-A-I. Under all the above conditions, the secreted apo-A-I exhibited similar isoform patterns in two-dimensional gel electrophoresis. These data show that both chick hepatocytes and human hepatoma cells are capable of intracellularly processing pro-apo-A-I to apo-A-I, and that the extent of intracellular processing is controlled by the cell's hormonal environment.     

Steroids and related products. LIV. The synthesis of 11-oxa steroids. VI. The synthesis of 11-oxatestosterone

The synthesis of 11-oxatestosterone from 11-oxa-5 alpha-androstane-3,17-dione, which is available from hecogenin, is described. The product shows, in comparison with the natural hormone, diminished androgenic and anabolic activities.     

Hydrogen peroxide formation and lipid peroxidation in rat uterus—effect of hormones and vitamin E

The effect of estradiol-17β and progesterone given separately as well as in combination on the rate of hydrogen peroxide formation and lipid peroxidation in the uteri of ovariectomized rats was studied. Estradiol in 3μg dose per day per animal elicited maximum stimulatory response and progesterone (100μg), on the other hand, was without any such effect. However, progesterone given along with estradiol completely prevented the effect due to the latter. In the same way, vitamin E, a well known antioxidant was found to be extremelv effective in protecting the uterus from the highly peroxidative action of estradiol-17β.     

Studies on the partial structure of the O-antigen of Vibrio cholera Ogawa G-2102

Detailed information was obtained regarding the partial structure of the lipopolysaccharide (LPS), containing glucose, glucuronic acid, 2-amino-2-deoxy-glucose, L-glycero-D-gluco-heptose, and small proportions of L-glycero-D-manno-heptose, mannose, and galactose, isolated from Vibrio cholera Ogawa G-2102. Structures of three oligosaccharides were determined. Results of deamination experiments established the sequence of the linkages between the amino sugar and heptose residues in the O-antigenic polysaccharide.     

A 43 kDa DNA binding protein from the pea chloroplast interacts with and stimulates the cognate DNA polymerase.

A DNA binding protein with DNA polymerase 'accessory activity' has been identified and purified to apparent homogeneity from pea chloroplasts. This protein consists of a single subunit of 43 kDa and binds to DNA regardless of its base sequence and topology. It increases cognate DNA polymerase-primase activity in a dose dependent manner. Using solid phase protein-protein interaction trapping and co-immunoprecipitation techniques, the purified protein was found to associate with the chloroplast DNA polymerase. The chloroplast DNA polymerase also binds directly to the radioiodinated 43 kDa protein. The specific interaction between 43 kDa protein and chloroplast DNA polymerase results in the synthesis of longer DNA chains. The 43 kDa protein, present abundantly in the pea chloroplast, appears to increase processivity of the chloroplast DNA polymerase and may play an important role in the replication of pea chloroplast DNA.     

A histidine binding protein ofEscherichia coli: a component of cystine binding protein ofEscherichia coli

Summary Commercially obtained cystine binding protein (CBP), an osmotic shock protein ofEscherichia coli, was studied in an effort to determine its binding characteristics. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS/PAGE) analysis of commercially obtained CBP showed three protein bands. N-terminal amino acid microsequencing and subsequent computer search revealed that the sequence of one of these proteins (25-kDa) was nearly identical to histidine binding protein (HisJ) ofSalmonella typhimurium. Purification of CBP by HPLC yielded four protein peaks, of which one bound histidine exclusively. Binding was maximal at pH 5.0 to 6.0, at 4°C, did not require calcium or magnesium ions and was not inhibited by reduction of CBP disulfide bonds. Amino acids other than histidine or cystine did not bind to CBP. These data show that commercially available CBP is not a homogenous protein; it contains a histidine as well as a cystine binding component.     

Mutations in tumour suppressor genes,l(2)gl andl(2)gd,alter the expression ofwingless inDrosophila

To understand the roles of two well known tumour suppressor genes.l(2)gl andl(2)gd in normal imaginal disc development inDrosophila, we have initiated a study to examine effect of mulations of these genes on the expression of genes involved in the patterning of the imaginal discs. In this study we show that the expression ofwingless, theDrosophila orthologue of the mammalian oncogeneWnt, is affected in the imaginal discs ofl(2)gl ⁴ andl(2)gd ¹ mutant individuals. In the tumourous wing imaginal discs froml(2)gl mutant larvae, the pattern ofwingless expression was progressively disrupted with an increase in the area of expression, Tumourous wing imaginal discs froml(2)gd homozygous individuals exhibited progressive broadening and extension of the wingless expressing domains. We suggest thatl(2)gl andl(2)gd might be involved in regulating post embryonic expression ofWingless.