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Biomedical subjects

A C Robinson

Publications and source records attributed to A C Robinson.

At least 55 records · Page 3Linked to original sources
PubMed1989

Circulating reproductive hormones and hypothalamic oestradiol and progestin receptors in infertile Zucker rats.

Plasma concentrations of LH, FSH, prolactin and progesterone were measured during the oestrous cycle in obese (fa/fa) and non obese (Fa/?) Zucker rats. In obese rats the mid-afternoon surge of LH during prooestrus was reduced compared with that in non-obese rats (P less than 0.05), and the maximum concentrations of FSH and prolactin declined more slowly during oestrus. Progesterone concentrations were higher during most of the oestrous cycle in obese rats. Oestradiol and progestin receptors were measured in the hypothalamus of female Zucker rats. Lower concentrations of oestradiol receptors were found in the preoptic area of obese rats (P less than 0.05). Concentrations of oestradiol receptors in the medial basal hypothalamus were also lower in obese rats, though the difference was not statistically significant. Concentrations of progestin receptors were similar in both phenotypes in the preoptic area and media basal hypothalamus. It seems likely that the abnormalities in reproductive hormones and oestradiol receptors contribute to the infertility of obese female Zucker rats. The underlying mechanism has still to be determined.

Animals↗
PubMed1989

The mechanism of ceruminolysis.

In a previous study comparing the efficacy of a selection of commonly used ceruminolytics, the authors noted that aqueous-based preparations, and in particular solutions of sodium bicarbonate, were more effective in disintegrating cerumen than most organic-based preparations. In that study, the authors also observed that not only had the wax truly disintegrated following exposure to the aqueous-based preparations, but also that a marked degree of swelling of the wax spheres had occurred with these preparations. In this paper the mechanism of ceruminolysis was investigated by means of a number of commonly available histological techniques. Our findings show that desquamated sheets of corneocytes are the major constituent of cerumen plugs and provide the structural framework of the wax bolus. Ceruminolytics work by hydrating the keratin cells of these sheets of desquamated stratum corneum and subsequently inducing keratolysis, with disintegration of the wax.

Antipyrine↗
PubMed1989

The efficacy of ceruminolytics: everything old is new again.

Impacted cerumen frequently poses a problem to both patients and physicians. Over the years, many topical ceruminolytics have been advocated, many of which are currently used with no scientific proof of their effectiveness. The effects of a variety of ceruminolytics were tested in vitro on standard spheres of normal human cerumen. The only truly effective ceruminolytics had an aqueous base, and the most effective ceruminolytic was a 10% solution of sodium bicarbonate. In contrast, those ceruminolytics which had an organic base, including most of the commonly available commercial preparations, had little ceruminolytic effect. When we consider that Joseph Toynbee recommended the use of sodium bicarbonate ear drops as a ceruminolytic in 1860, then surely, when looking for the ideal ceruminolytic, "everything old is new again".

Bicarbonates↗
PubMed1989

Anterior skull defect reconstruction with methyl methacrylate.

A case of squamous cell carcinoma of the fronto-ethmoid complex in an 18-year-old man is presented. At the time of resection both the anterior and posterior tables of the frontal sinus had to be removed. The resulting surgical defect left a marked cosmetic deformity. CT scan five months after the resection suggested calcification with possible ossification of the dura. Exploration of the area confirmed these findings. Because of the firmness of the dura it was possible to contour a methyl methacrylate template to fill the defect. This was wired to the surrounding bone and provided an excellent cosmetic result. The principle of dural osteogenesis is described, and cranioplasty methods are reviewed.

Adolescent↗
PubMed1988

Mapping and characterization of mutants of the Escherichia coli cell division gene, ftsA.

Eight independent temperature-sensitive mutants of the cell division protein FtsA have been studied. They fall into two classes in terms of their behaviour at 42 degrees C and recovery at 30 degrees C. The first class shows salt-dependent temperature-sensitivity and reversible inactivation of FtsA protein at 42 degrees C. The second shows irreversible inactivation which is not prevented by salt. Recovery of the ability to divide at 30 degrees C is rapid in mutants of the first group, but is delayed for approximately a generation time in the second group. This suggests that irreversible inactivation of FtsA causes extensive damage to the division machinery. The amino acid substitutions show clustering to a limited domain of the protein, and one particular substitution is found in three of the mutants.

Alleles↗
PubMed1988

Thyroid function in male Zucker rats exposed to cold.

Non-obese and obese Zucker rats were exposed to 6 degrees C for 20 days. At the end of the experiment thyroid stimulating hormone (TSH), circulating thyroid hormones, and the weights of the thyroid gland and a brown adipose tissue pad were measured. TSH and 3,5,3'-triiodothyronine concentrations and brown adipose tissue weights increased in response to cold in both phenotypes but by larger amounts in obese rats. Free thyroxine was lower in obese rats. There appears to be no defect in thyroid function in congenitally obese rats exposed to cold, or in their ability to develop brown adipose tissue.

Adipose Tissue, Brown↗
PubMed1987

Iron-molybdenum cofactor biosynthesis in Azotobacter vinelandii requires the iron protein of nitrogenase.

Nitrogenase is composed of two separately purified proteins called the Fe protein and the MoFe protein. In Azotobacter vinelandii the genes encoding these structural components are clustered and ordered: nifH (Fe protein)-nifD (MoFe protein alpha subunit)-nifK (MoFe protein beta subunit). The MoFe protein contains an ironmolybdenum cofactor (FeMo cofactor) whose biosynthesis involves the participation of at least five gene products, nifQ, nifB, nifN, nifE, and nifV. In this study an A. vinelandii mutant strain, which contains a defined deletion within the nifH (Fe protein) gene, was isolated and studied. This mutant is still able to accumulate significant amounts of MoFe protein subunits. However, extracts of this nifH deletion strain have only very low levels of MoFe protein acetylene reduction activity. Fully active MoFe protein can be reconstituted by simply adding isolated FeMo cofactor to the extracts. Fe protein is not necessary to stabilize or insert this preformed FeMo cofactor into the FeMo cofactor-deficient MoFe protein synthesized by the nifH deletion strain. Extracts of the nifH deletion strain can carry out molybdate and ATP-dependent in vitro FeMo cofactor biosynthesis provided Fe protein is added, demonstrating that they contain the products encoded by the FeMo cofactor biosynthetic genes. These data demonstrate that the Fe protein is physically required for the biosynthesis of FeMo cofactor in A. vinelandii.

Azotobacter↗
PubMed1987

Inactivation of pea seed glutamine synthetase by the toxin, tabtoxinine-beta-lactam.

Glutamine synthetase of plants is the physiological target of tabtoxinine-beta-lactam, a toxin produced by several disease-causing pathovars of Pseudomonas syringae. This toxin, a unique amino acid, is an active site-directed, irreversible inhibitor of glutamine synthetase from pea. ATP is required for inactivation. Neither ADP, AMP, nor adenosine 5'-(beta,gamma-methylene)triphosphate (AMP-PCP) supports inactivation. Adenyl-5'-yl imidophosphate (AMP-PNP) is slowly hydrolyzed by glutamine synthetase to produce adenyl-5'-yl phosphoramidate (AMP-PN) and inorganic phosphate as identified by 31P NMR spectroscopic analysis. AMP-PNP also supports a slow inactivation of glutamine synthetase by tabtoxinine-beta-lactam. These data are consistent with gamma-phosphate transfer being involved in the inactivation. Completely inactivated glutamine synthetase has 0.9 mumol of toxin bound/mumol of subunit. One mumol of ATP is bound per mumol of subunit of glutamine synthetase in the absence of either the toxin or another active site-directed inhibitor, methionine sulfoximine; whereas, a 2nd mumol of either [alpha- or gamma-32P]ATP is bound per mumol of subunit when glutamine synthetase is incubated in the presence of either toxin or methionine sulfoximine until all enzyme activity is lost. These data suggest that the gamma-phosphate hydrolyzed from ATP during inactivation remains with the enzyme-inhibitor complex, as well as the ADP. The open chain form, tabtoxinine, was neither a reversible nor an irreversible inhibitor of glutamine synthetase, suggesting that the beta-lactam ring is necessary for inhibition. The inactivation of glutamine synthetase with tabtoxinine-beta-lactam is pseudo-first-order when done in buffer containing 15% (v/v) ethylene glycol. The rate constant for this reaction is 3 X 10(-2) S-1, and the Ki for the toxin is 1 mM. Removal of the ethylene glycol from the buffer allows the reaction to proceed in a non-first-order manner with the apparent rate constant decreasing with time. As the enzyme is inactivated in these conditions, the binding affinity for the toxin appears to decrease, while the Km observed for glutamate does not change.

Adenosine Diphosphate↗
PubMed1986

Activity, reconstitution, and accumulation of nitrogenase components in Azotobacter vinelandii mutant strains containing defined deletions within the nitrogenase structural gene cluster.

The Azotobacter vinelandii genes encoding the nitrogenase structural components are clustered and ordered: nifH (Fe protein)-nifD (MoFe protein alpha subunit)-nifK (MoFe protein beta subunit). In this study various A. vinelandii mutant strains which contain defined deletions within the nitrogenase structural genes were isolated and studied. Mutants deleted for the nifD or nifK genes were still able to accumulate significant amounts of the unaltered MoFe protein subunit as well as active Fe protein. Extracts of such nifD or nifK deletion strains had no MoFe protein activity. However, active MoFe protein could be reconstituted by mixing extracts of the mutant strains. These results establish an approach for the purification of the individual MoFe protein subunits. Mutants lacking either or both of the MoFe protein subunits were still able to synthesize the iron-molybdenum cofactor (FeMo-cofactor), indicating that in A. vinelandii the FeMo-cofactor is preassembled and inserted into the MoFe protein. In contrast, a mutant strain lacking both the Fe protein and the MoFe protein failed to accumulate any detectable FeMo-cofactor. The further utility of specifically altered A. vinelandii strains for the study of the assembly, structure, and reactivity of nitrogenase is discussed.

Azotobacter↗
PubMed1986

Further evidence for overlapping transcriptional units in an Escherichia coli cell envelope-cell division gene cluster: DNA sequence and transcriptional organization of the ddl ftsQ region.

A 1.2-kilobase-pair BamHI fragment from a cell envelope-cell division gene cluster of Escherichia coli containing ddl and part of ftsQ was cloned and sequenced, and the sequence was interpreted with the aid of genetic complementation and promoter fusion data for the region. Both ddl and ftsQ were transcribed in the same direction (clockwise on the genetic map). ddl was shown to be capable of independent expression from a promoter of its own, and a promoter was identified within the ddl structural gene. The structural gene of ddl consisted of 918 nucleotides, encoding a 306-residue polypeptide of molecular weight 32,840; the synthesis of a protein of this molecular weight was shown to be directed from the 1.2-kilobase-pair BamHI fragment in minicells. Analysis of the DNA sequence further showed that the termination codon of ddl is separated from the initiation codon of ftsQ by one base, which suggests that these two genes may be translationally coupled when transcription is initiated upstream of ddl. This represents a second instance of potential translational coupling within this gene cluster and also indicates that the ddl and ftsQ transcriptional units must overlap (as has been reported earlier for ftsQ and ftsA and for ftsA and ftsZ).

Base Sequence↗
PubMed1984

Serious burns sustained from wearing saris.

Two cases are reported in which patients have received burns following the accidental ignition of saris. This paper stresses the danger of these garments in the presence of a naked flame.

Accidents, Home↗
PubMed1984

DNA sequence and transcriptional organization of essential cell division genes ftsQ and ftsA of Escherichia coli: evidence for overlapping transcriptional units.

The DNA sequence of a cloned segment of the Escherichia coli chromosome containing ftsQ, ftsA, and part of the ftsZ gene was determined and interpreted for genetic complementation and promoter fusion data for the region. The contiguous genes ftsQ, ftsA, and ftsZ were transcribed in the same direction (clockwise on the genetic map) and each had at least one associated promoter which allowed it to be transcribed independently of neighboring genes. ftsA and ftsZ possessed promoters within the coding sequences of the juxtaposed upstream structural genes, and a promoter element for ftsA was surrounded by a region of twofold symmetry which corresponded closely to a symmetrical element in the region of a putative ftsZ promoter. The structural gene of ftsQ consisted of 838 nucleotides, encoding a 276-residue amino acid polypeptide of molecular weight 31,400; the structural gene of ftsA consisted of 1,260 nucleotides, encoding a 420-residue amino acid polypeptide of molecular weight 45,400. The observation that the termination codon of ftsQ overlaps with a potential initiation codon for ftsA suggested that these two genes may be translationally coupled when transcription is initiated upstream of the ftsQ coding sequence.

Amino Acid Sequence↗