PubMed Health⌕ Search

Biomedical subjects

K E Ebner

Publications and source records attributed to K E Ebner.

At least 55 records · Page 3Linked to original sources
PubMed1979

Reaction of the histidines of prolactin with ethoxyformic anhydride. A binding site modification.

The seven histidines of bovine prolactin were modified with ethoxyformic anhydride and two classes of reactivity were apparent: 5 histidines were in the more reactive class (k = 0.097 min-1) and 2 histidines were less reactive (k = 0.011 min-1). The activity of the modified prolactins was determined by measuring their ability to bind to prolactin receptors from rabbit mammary glands. This assay showed that prolactin was fully active when 0 to 5 histidines were modified. If all 7 residues were modified, the hormone was unable to bind to its receptor. Circular dichroism studies indicated no significant differences in conformation for prolactins which had 2 to 7 histidines modified. Modification of human growth hormone and human placental lactogen with ethoxyformic anhydride resulted in a loss of the ability of these lactogenic hormones to bind to the prolactin receptor. For all three hormones, essentially full activity was recovered when the modifying group was removed by treatment with hydroxylamine. Sequence comparisons indicate that only 2 of the 3 growth hormone histidines and 2 of 7 placental lactogen histidines were homologous with histidines in bovine prolactin and that, in each case, they correspond to His-27 and His-30 in bovine prolactin. It is postulated that these residues serve to identify a portion of the binding domain of bovine prolactin.

Amino Acid Sequence↗
PubMed1979

Isolation and characterization of alpha-lactalbumin from a rat mammary tumor.

alpha-Lactalbumin was purified to homogeneity from the R3230AC rat mammary adenocarcinoma. alpha-Lactalbumin from the R3230AC tumor had the same amino acid and carbohydrate composition, migration on gel electrophoresis, and specific activity as did alpha-lactalbumin isolated from normal rat milk.

Adenocarcinoma↗
PubMed1978

Coupled cell-free synthesis, segregation, and core glycosylation of a secretory protein.

mRNA from rat mammary glands 13-15 days post partum was translated in a wheat germ cell-free system either in the absence or in the presence of ribosome-denuded membranes prepared from isolated rough microsomes of dog pancreas. Newly synthesized alpha-lactalbumin was identified by immunoprecipitation with a monospecific rabbit antiserum against rat alpha-lactalbumin and was characterized by partial amino-terminal sequence determination and by lectin affinity chromatography. In the absence of membranes a presumably unglycosylated form of alpha-lactalbumin was synthesized that bound neither to concanavalin A-Sepharose nor to Ricinus communis lectin-agarose and that contained an amino-terminal signal peptide region comprising 19 amino acid residues. In the presence of membranes a processed form was synthesized that lacked the signal peptide portion and that had an amino-terminal sequence identical to that of mature alpha-lactalbumin. Furthermore, this processed form was found to be segregated, presumably within the microsomal vesicles, because it was resistant to post-translational proteolysis. It was also found to be glycosylated, and because it bound to concanavalin A-Sepharose, from which it could be eluted specifically by alpha-methyl mannoside, but not to R. communis lectin-agarose, it was presumably core-glycosylated. Processing, segregation, and core glycosylation were observed to proceed only when membranes were present during translation and not when they were added after translation.

Amino Acid Sequence↗
PubMed1977

Competition of delta 9-tetrahydrocannabinol with estrogen in rat uterine estrogen receptor binding.

Direct competition experiments with delta 9 -tetrahydrocannibinol (delta 9-THC) and estradiol in binding assays with rat uterine cytosol estrogen receptors showed that delta 9-THC was a weak, but nevertheless significant, competitor for binding to cytoplasmic estrogen receptors. These data support, at the molecular level, the observations that delta 9-THC has a weak estrogenic activity (at least the ability to bind to estrogen receptors). Moreover, estrogen-like binding suggests that delta 9-THC, acting at the level of estrogen receptor, causes a primary estrogenic effect rather than an indirect or secondary phenomenon.

Animals↗
PubMed1977

Incorporation of galactose into galactosyltransferase.

Bovine skim milk galactosyltransferase (EC 2.4.1.22) retained its catalytic activity after partial enzymatic removal of sialic acid and galactose. Desialylated and degalactosylated galactosyltransferase was a galactosyl acceptor in the galactosyltransferase reaction. [14C]Galactose from UDP-[14C]galactose was incorporated into the carbohydrate-depleted galactosyltransferase by native galactosyltransferase. The results suggest that galactosyltransferase participates in the biosynthesis of its glycopeptides of the sialic acid-galactose-N-acetylglucosamine type.

Animals↗
PubMed1977

Isolation and characterization of rat alpha-lactalbumin: a glycoprotein.

alpha-Lactalbumin was purified to homogeneity from rat milk. Rat alpha-lactalbumin, in contrast to other alpha-lactalbumins, is a glycoprotein and exhibits an abnormally high molecular weight when obtained by gel filtration or electrophoresis in sodium dodecyl sulfate. The molecular weight by sedimentation equilibrium is 15 400 +/- 5% and of the reduced and alkylated protein is 16 000 when determined by thin-layer chromatography in 6 M guanidine hydrochloride. At least, three major charge forms, all containing carbohydrate and active in the lactose synthetase reaction were demonstrated. The amino acid composition reveals a high proline content which is reflected in a low alpha-helical content.

Amino Acids↗
PubMed1977

Inhibition and inactivation of bovine mammary and liver UDP-galactose-4-epimerases.

Bovine liver and mammary UDP-galactose-4-epimerases were investigated with respect to various inhibitors and inactivators. Uridine nucleotides and NADH are potent inhibitors with Ki values in the low micromolar range. The NAD+/NADH ratio may be an important physiological control mechanism for it affects markedly the activity of the enzyme with 50% inhibition occurring at a ratio of 20:1. In the presence of uridine nucleotides binding of NADH to the epimerases is enhanced. Consequently, the effect of changes in the NAD+/NADH ratio in vivo would not be immediately apparent as uridine nucleotides would slow down the displacement of NADH by NAD+. Neither uridine nor galactose 1-phosphate inhibits the purified enzymes as previously reported with the impure liver enzyme. Uridine nucleotides provide almost total protection against the apparent first order inactivation of the epimerases by trypsin and allow determination of dissociation constants. NAD+ partially protects against trypsin inactivation. Inactivation with various sulfhydryl reagents is complex and the results indicate that at least three sulfhydryl groups may be modified before total inactivation occurs. Partial inactivation occurs upon modification of the epimerases with 2-hydroxy-5-nitrogenzyl bromide. Some protection against this modification is provided by the combination of NAD+ and UDP.

Animals↗
PubMed1977

Purification and characterization of UDP-galactose-4-epimerase from bovine tissues.

Bovine liver and mammary UDP-galactose-4-epimerases have been purified to apparent electrophoretic homogeneity by a simple procedure involving the use of two affinity adsorbants, UDP-hexanolamine-Sepharose and NAD+-hexanolamine-Sepharose. The bovine thyroid epimerase has been partially purified by the same procedure. All three enzymes require NAD+ for activity, and all have a similar apparent molecular weight of approximately 40,000 as determined by gel filtration of the active enzymes. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the liver and mammary epimerases revealed similar molecular weights of 37,000 for both enzymes thus indicating that neither protein was dimeric. During development of the isolation procedure conditions were determined which would stabilize enzymatic activity in very dilute solutions. The liver and mammary enzymes, although similar in some respects, differed in amino acid composition and specific activity.

Amino Acids↗
PubMed1977

alpha-Lactalbumin levels in human mammary tumors, sera, and mammary cell culture lines.

Antiserum to purified human alpha-lactalbumin was produced in rabbits and used to develop a radioimmunoassay capable of detecting 0.1 ng of alpha-lactalbumin per ml of sample. Human breast diseases were analyzed for alpha-lactalbumin levels. A high percentage of breast carcinomas contained varying levels of alpha-lactalbumin. Lymph node metastases from primary carcinomas that synthesized alpha-lactalbumin also contained it. Analysis of serum from breast cancer patients indicated that approximately 25 percent had measurable levels of alpha-lactalbumin before surgery, but no alpha-lactalbumin was found in postsurgery sera. alpha-Lactalbumin was not detected in the urine of early lactational women, although it was present in the sera. Human cell culture lines derived from pleural effusions of mammary carcinomas contained little, if any, alpha-lactalbumin. Other human cell lines derived from mammary carcinomas and grown as solid tumors in athymic mice did not contain measurable levels of alpha-lactalbumin.

Breast Neoplasms↗
PubMed1976

Ultraviolet photoinactivation of galactosyltransferase. Protection by substrates.

Galactosyltransferase was irreversibly inactivated upon exposure to ultraviolet light and the rate of inactivation followed apparent first-order kinetics. Significant protection against inactivation was observed in the presence of various combinations of substrates. UDPgalactose and Mn2+ together gave the most protection. Amino acid analyses revealed the loss of 1 mol of tryptophan per mol of galactosyltransferase upon ultraviolet photoinactivation. Further evidence for an essential trypotphan was provided by difference spectra and by inactivation with 2-hydroxy-5-nitrobenzyl bromide and protection against this reagent by Mn2+ and UDPgalactose. The protection by UDPgalactose and Mn2+ was greater than that provided by UDPgalactose alone. Since Mn2+ provided no protection by itself, this suggested that the formation of the galactosyltransferase-Mn2+-UDPgalactose complex caused a conformational change which was responsible for the observed protection of the essential tryptophanyl residue.

Amino Acids↗
PubMed1976

Nomemclature of the proteins of cow's milk: fourth revision.

This report reviews the nomenclature of the milk proteins of cow's milk in light of more recent advances in our knowledge. With the establishment of the primary structures of a number of these proteins, we now have a definite identification of alphas1-, kappa-, beta-, and the gamma-caseins as well as beta-lactoglobulin and alpha-lactalbumin. On the basis of new information on their primary structures and relationship to beta-casein polymorphs, changes in nomenclature have been recommended for proteins of the gamma-casein fraction. Although the primary structure serves as the unambiguous definition of proteins for which it is known, a more practical identification is necessary. We recommend that their behavior in gel electrophoresis under suitable conditions be employed for this purpose for all of the "major" milk proteins of raw skim milk except the immunoglobulins where, because of their heterogeneity and molecular genetics, physical parameters are less useful and their identification must be based upon antigenic determinants and their homology with their human counterparts. More work is needed and, with the accumulation of more information, additional changes in nomenclature can be expected for such proteins as the minor components of alphas- and kappa-caseins, alpha-lactalbumin, and the proteose-peptone fraction as well as further confirmation of the presence of immunoglobulins IgE and additional IgG subclasses. Additional components and genetic variants also can be expected.

Animals↗