Biomedical subjects

D R Headon

Publications and source records attributed to D R Headon.

At least 37 records · Page 2Linked to original sources

PubMed1993

Enzymes in the animal-feed industry.

The increasing economic pressures currently being placed upon animal producers demand more-efficient utilization of low-grade feedstuffs. In addition, consumer awareness and new legislation require that any increase in animal production cannot be achieved via growth-promoting drugs or other chemical substances. One increasingly popular approach to this problem is to supplement animal diets with hydrolytic enzymes in an attempt to aid the digestion and absorption of poorly available nutrients, or to remove antinutritional factors from the diet. Concerns raised by this practice include the ability of such enzymes to survive processing temperatures and even the animals' digestive tract.

Animal Feed↗

PubMed1993

Active immunization of heifers against a synthetic fragment of bovine inhibin.

Two experiments were conducted in cyclic beef heifers to determine whether active immunization against bovine inhibin alpha 1-26 Gly-Tyr (bINH) affected follicular dynamics, hormone concentration or ovulation rate. In Expt 1, heifers (n = 9) were actively immunized against bINH conjugated to human alpha globulins (HAG) using bis-diazotized benzidine in non-ulcerative Freund's adjuvant (NUFA; primary on day 0; booster injections on days 53, 84 and 116 using conjugated bINH and on days 176 and 366 using unconjugated bINH; ten heifers were used as controls). Ovaries were examined daily using ultrasound scanning (days 70-155 and 384-391) and corresponding blood samples were collected for bINH antibody titre, luteinizing hormone (LH), follicle-stimulating hormone (FSH) and oestradiol determinations. Four treated and four control heifers were injected with 10 micrograms gonadotrophin-releasing hormone (GnRH) on day 386 (day 2 of the oestrous cycle). Although bINH-immunized heifers had variable antibody titres ranging from 4 to 50% I125-labelled bINH bound to serum diluted 1:2000, ovulation rate was unaffected. In oestrous cycles with three dominant follicles, the ovulatory follicles grew faster (2.5 +/- 0.2 versus 1.6 +/- 0.3 mm day-1; mean +/- SEM), had shorter durations of growth (5.7 +/- 0.8 versus 9.6 +/- 1.6 days) and duration of detection (7.5 +/- 0.8 versus 12.0 +/- 2.4 days) in immunized heifers. Mean concentrations of FSH, LH and oestradiol were unaltered in most cases during oestrous cycles in bINH-immunized compared with control heifers. There was no significant difference in the percentage increase in FSH or LH, after GnRH injection, between control and immunized heifers. As ovulation rate was unaltered in the first experiment, a second similar study was designed using a different immunization protocol. In Expt 2, heifers were immunized with bINH conjugated to human serum albumin using glutaraldehyde with the following doses: 0.0 (control; n = 7), 0.33 (n = 7), 1.0 (n = 8) and 3.0 (n = 7) mg. Three booster immunizations were given 33, 66 and 209 days after primary immunization. Immunization increased the number of oestrous cycles with multiple ovulations (42 of 132 (32%) oestrous cycles examined) compared with controls (1 of 30 (3.3%) oestrous cycles examined). Neither titre nor ovulation rate was affected by dose of bINH used. In summary, following bINH immunization, ovulation rate was not increased despite changes in follicular dynamics in Expt 1, but was increased in 32% of oestrous cycles in Expt 2.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1992

Structural organization of the mouse lactoferrin gene.

The complete structure of the mouse lactoferrin gene is presented. Mouse lactoferrin (mLF) is encoded by a single copy gene of approximately 30 kilobases (kb) in size. The gene is organized into 17 exons separated by 16 introns. The exons range in size from 48 base pairs (bp) to 190 bp whereas the introns range from 0.2 kb to 4.3 kb. Structural analysis of the mouse lactoferrin gene reveals that this gene shares a similar intron-exon distribution pattern with both human transferrin and chicken ovotransferrin.

Animals↗

PubMed1992

An inducible expression system for the production of human lactoferrin in Aspergillus nidulans.

The production and secretion of human lactoferrin (hLF) in Aspergillus nidulans is described. The hLF cDNA was expressed under the control of the strong ethanol-inducible alcohol dehydrogenase (alcA) promoter. Recombinant hLF (re-hLF) is produced at levels up to 5 micrograms/ml. Approximately 30% of the re-hLF produced in this system is secreted into the growth medium. The re-hLF is indistinguishable from native hLF with respect to size and immunoreactivity. Furthermore, re-hLF is functional by the criterion of iron-binding capacity. The A. nidulans expression system offers an inexpensive, convenient method for the controlled production of mg amounts of biologically active mammalian glycoproteins.

Aspergillus nidulans↗

PubMed1992

Nucleotide and primary amino acid sequence of porcine lactoferrin.

A cDNA encoding porcine lactoferrin (pLF) was isolated from a porcine mammary gland lambda gt11 cDNA library using human lactoferrin cDNA as the hybridization probe. Nucleotide sequence analysis indicates that pLF is 686 amino acids in length and shares 72.6%, 70.7% and 62.2% overall amino acid sequence identity with bovine, human and murine lactoferrin, respectively.

Amino Acid Sequence↗

PubMed1992

Production of biologically active recombinant human lactoferrin in Aspergillus oryzae.

We report the production of recombinant human lactoferrin in Aspergillus oryzae. Expression of human lactoferrin (hLF), a 78 kD glycoprotein, was achieved by placing the cDNA under the control of the A. oryzae alpha-amylase promoter and the 3' flanking region of the A. niger glucoamylase gene. Using this system, hLF is expressed and secreted into the growth medium at levels up to 25 mg/l. The recombinant lactoferrin is indistinguishable from human milk lactoferrin with respect to its size, immunoreactivity, and iron-binding capacity. The recombinant protein appears to be appropriately N-linked glycosylated and correctly processed at the N-terminus by the A. oryzae secretory apparatus. Lactoferrin is the largest heterologous protein and the first mammalian glycoprotein expressed in the Aspergillus system to date. Hence, this expression system appears suitable for the large-scale production and secretion of biologically active mammalian glycoproteins.

Amino Acid Sequence↗

PubMed1986

Fatty acyl composition of the major lipid classes of HDL2 and HDL3 of human serum.

High density lipoprotein subfractions 2 and 3 were isolated from the sera of normolipidaemic males by rate zonal ultracentrifugation. The fatty acyl compositions of their major lipid classes--phospholipids, cholesteryl esters and triacylglycerols--were determined. The average chain length and degree of unsaturation of the fatty acyl components of the phospholipids and cholesteryl esters of the HDL3 subfraction were found to be significantly higher than those of the HDL2 subfraction. The triacylglycerol moieties of the HDL3 subfraction had a higher proportion of unsaturated fatty acyl components than HDL2, but there was no difference in the average chain length between the two subfractions. These results are not consistent with an equilibration of the lipid components between the two HDL subfractions, as would be expected from the results of tracer studies. A role for the fatty acyl composition of high density lipoproteins in the determination of high density lipoprotein subfraction distribution is proposed.

Adult↗

PubMed1986

Corticotropin specifically stimulates the uptake and intracellular movements of sterol carrier protein in adrenals.

Sterol carrier protein (SCP), also known as liver fatty acid binding protein, is a major adrenal protein localized in the cytosol and inner mitochondrial membrane. SCP is synthesized in liver and intestine and then rapidly secreted into blood, where it associates primarily with the high density lipoprotein fraction. Studies using steroidogenesis inhibitors showed that corticotropin has a specific effect on the uptake of SCP and its movement with cholesterol to the inner mitochondrial membrane. Thus, SCP appears to be intimately involved in the mechanism(s) of adrenal steroidogenesis from cholesterol.

Adrenal Cortex↗

PubMed1984

Intramitochondrial movement of adrenal sterol carrier protein with cholesterol in response to corticotropin.

Sterol carrier protein (SCP) is a highly abundant, ubiquitous, low molecular weight protein that has a rapid turnover and multifunctional roles in lipid metabolism and transport. It is also known as the fatty acid-binding protein. These and other characteristics led to studies on the possible role of SCP in mediation of steroidogenic responses of the adrenal gland to corticotropin. To quantitate the level of SCP in adrenal tissue and subcellular fractions, a specific immunochemical assay was developed using an antibody to homogeneous liver SCP. SCP is a major protein in adrenal cells (greater than 100 micrograms/mg of total protein). The bulk of it is present in the soluble (60%) and mitochondrial (35%) fractions. Nearly all mitochondrial SCP is present in the inner membrane. Adrenal SCP undergoes a dramatic diurnal variation, varying from 2% to 12% of total protein. When corticotropin was administered in vivo in the presence of aminoglutethimide, an inhibitor of steroidogenesis, there was a parallel movement of SCP with cholesterol to the inner mitochondrial membrane. Other work showed mitochondrial SCP levels increase only in situations where there is an increase in cholesterol levels. These findings strongly suggest that one of the functions of adrenal SCP is to participate in teh corticotropin-stimulated movement of cholesterol to the inner mitochondrial membrane for steroidogenesis.

Adrenal Glands↗

PubMed1984

Molecular cloning of a cDNA for the chicken progesterone receptor B antigen.

A cDNA for the chicken progesterone receptor B subunit antigen (Mr, 108,000) has been isolated from a cDNA library prepared from size-selected chicken oviduct poly(A)+RNA. A specific monoclonal antibody raised against hen progesterone receptor B subunit (alpha PR-B) was used to screen the library. Recombinant clones reacting with the antibody by virtue of antigen expression were used in hybrid-selected translation. A single clone, pPRB-1, hybridized specifically to a mRNA that yielded a Mr 108,000 protein when translated in vitro and which was immunoprecipitable by the alpha PR-B antibody. This cDNA represents a 470-base-pair portion of the PR-B nucleotide sequence. Additional clones have been subsequently isolated from the recombinant library using the insert from pPRB-1 as a specific probe. A mRNA size of approximately 3000 nucleotides was determined for the chicken progesterone receptor B subunit by formaldehyde/agarose gel electrophoresis and blot hybridization using pPRB-1 as a probe. Preliminary studies show that withdrawal of hormone from chickens treated chronically with estrogen leads to a dramatic decrease in the cellular RNA concentration of receptor B, indicating that target tissue levels of receptor B RNA are under hormonal control.

Animals↗

PubMed1984

Translation in Xenopus oocytes of messenger RNA from A431 cells for human epidermal growth factor receptor proteins.

Translation of messenger RNAs (mRNAs) for human epidermal growth factor receptor (EGF-R) proteins was accomplished in a Xenopus oocyte translation system. Translation of these mRNAs in rabbit reticulocyte lysates and wheat germ extracts were unsuccessful, in accordance with the general difficulty in translating mRNAs for membrane-bound glycoproteins in conventional heterologous cell-free systems. Total poly(A)+RNA from a human epidermoid carcinoma cell line A431 was injected into oocytes from Xenopus laevis. After incubation in the presence of [35S]methionine, the oocytes were homogenized and the supernatant incubated with several different polyclonal antibodies (IgGs) against the human EGF-R. Immunocomplexes were bound to protein A-Sepharose, washed extensively, and electrophoresed in sodium dodecyl sulfate-polyacrylamide gels. A protein of Mr = 160,000, corresponding to the EGF-R glycoprotein, was specifically precipitated from RNA-injected oocytes by each of the anti-EGF-R IgGs. This protein was not detectable in the immunoprecipitates from uninjected oocytes nor was it precipitated from RNA-injected oocytes by IgG from normal rabbit serum or IgG to an unrelated protein. A second protein of Mr = 100,000 was also immunoprecipitated from the homogenates of RNA-injected oocytes. This product corresponds to the EGF-R-related protein, present in A431 cells, which is structurally similar to the EGF-R (Weber et al., 1984). Thus, frog oocytes provide an efficient and generally applicable heterologous system for translation of mRNAs for large glycoproteins such as growth factor receptors. In addition, successful immunoprecipitation of translated products in this system provides a method for assay of mRNAs where biological activity of the proteins cannot be monitored.

Animals↗

PubMed1983

Distribution of membrane cholesterol of adrenal cortical cells after corticotropin stimulation.

Membrane cholesterol in adrenal cortical cells is enriched in the plasma membrane. Stimulation of isolated adrenal cortical cells with corticotropin leads to the production of corticosterone. At high levels of corticotropin, cholesterol for corticosterone synthesis arises by hydrolysis of cellular cholesteryl ester, whereas at lower levels of corticotropin cholesteryl ester levels are unchanged from control values and there is a decrease in plasma-membrane cholesterol levels.

Adrenal Cortex↗

PubMed1980

The differential release of basal ATPase, Ca2+-dependent ATPase, 5'-nucleotidase and cholesterol during homogenization of skeletal muscle.

The influence of homogenization times on the presence of constituents in the microsomal fraction of skeletal muscle was investigated. Membranes having Ca2+-activated ATPase activity have a fragmentation pattern distinct from that of membranes displaying Ca2+-independent or basal ATPase activity. These latter membranes were found in highest specific concentration in the microsomal fraction prepared from homogenates subjected to short periods of homogenization. 5'-Nucleotidase (EC 3.1.3.5) activity paralleled that of basal ATPase on short periods of homogenization, as also did the specific concentration of cholesterol. Longer periods of homogenization led to a decrease in the specific activity of basal atpase, which reached its lowest value at 120s of homogenization, whereas the specific activity of 5'-nucleotidase and the specific concentration of cholesterol decreased initially in a similar manner to basal ATPase, but both increased substantially after the longest period of homogenization.

Adenosine Triphosphatases↗

PubMed1980

The role of commercial bovine serum albumin preparations in the culture of one-cell rabbit embryos to blastocysts.

Normal bovine serum albumin (BSA) in a complete medium without energy substrates promoted growth of 1-cell embryos to hatched blastocysts. Defatted charcoal-treated BSA did not promote growth to the blastocyst stage but the addition of pyruvate or palmitic and oleic acids allowed blastocyst growth but not blastocyst hatching. Sodium dodecyl sulphate-gel electrophoresis showed that both the normal and defatted BSA samples were heavily contaminated by proteins other than albumin. Fractionation of the normal BSA on Sephadex G-200 indicated that the property of promoting complete blastocyst hatching was not due to the albumin but was associated with the higher mol. wt fraction of the BSA. Extraction of normal BSA with chloroform appeared to destroy the hatching-promoting ability as neither the residue after extraction nor defatted BSA to which the organic extractate had been added promoted complete blastocyst hatching. It is concluded that commercial BSA may have at least two effects on blastocyst growth: (1) energy provision via albumin-bound fatty acids, and (2) promotion of blastocyst hatching by a non-albumin component.

Animals↗

PubMed1979