Biomedical subjects
Publications and source records attributed to K Edwards.
The nucleotide sequence of th 16S-23S spacer from a ribosomal RNA operon of Zea mays chloroplast DNA has been determined. It contains two tRNA genes, coding for tRNAlle (AUCU) and tRNAAla (GCGA), which are split by intervening sequences of 949 and 806 base pairs, respectively. Homology between the two introns suggests that they have a common origin.
The sequence of radioactively labelled amino acids at the N-terminus of proalbumin was determined by automated Edman-degradation. [3H] Valine, [3H]phenylalanine or [14C]arginine was incorporated into protein in vivo for a time period of 10 min after injection. Since albumin remains unlabelled during this time period (Urban et al., 1976), separation of proalbumin and albumin was not required for this work. Hence, compared to previous methods, a shorter purification procedure could be used which increased the yield of anti-albumin-precipitable protein and reduced the risk of proteolysis. Microsomes were prepared from livers removed 10 min after injection of the radioactively labelled amino acids. A buffer extract of the acetone-dried powder from these microsomes was chromatographed on DEAE-cellulose. All protein obtained after chromatography which could be precipitated with antiserum to serum albumin was isolated by immunoprecipitation and subsequent separation of the antigen-antibody complex. The sequence of radioactive amino acids in this antigen preparation suggests that about 20-25% of proalbumin possessed at the N-terminus the pentapeptide sequence X-Val-Phe-Arg-Arg- whereas 75-80% contained the hexapeptide sequence Arg-X-Val-Phe-Arg-Arg-.
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Adenine nucleotide levels could be precisely and reproducibly adjusted in liver cell suspensions by partially depleting the ATP pool with D-fructose or glycerol. Thus, it was possible to quantitatively correlate rates of protein synthesis and secretion with intracellular levels of ATP and with derived parameters, such as the adenylate energy charge. Half the maximum rate of incorporation of leucine into protein was observed at an energy charge of 0.80, a ratio of ATP to ADP of 2.6, and an ATP level of 1.05 mumol per g of wet cells. Proteins were secreted with half the maximum rate at an energy charge of 0.85, a ratio of ATP to ADP of 3.1 and an ATP concentration of 1.1 mumol per g of wet cells. Protein secretion did not depend on continued synthesis. Inhibitors of oxidative phosphorylation inhibited protein secretion in addition to protein synthesis, in contrast to observations by other authors on liver slices.
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Four infants with group B streptococcal meningitis had a delayed response to antibiotic therapy. Resolution of cerebrospinal fluid infection and/or pleocytosis occurred only after prolonged and intensive antimicrobial management. In this respect, these infants were similar to infants with gram-negative enteric meningitis. It is suggested that infants with group B streptococcal meningitis be closely monitored to insure adequate response to therapy.
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The complications of smallpox vaccination are reviewed. A case of disseminated vaccinia is presented. It is suggested that patients with sunburn may be susceptible to the complications of smallpox vaccination.
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DNA from the chicken genome was analysed both by isopycnic centrifugation in cesium salt density gradients and by reassociation analysis using hydroxyapatite (HAP) chromatography. Centrifugation in neutral CsCl revealed a single non-Gaussian band skewed toward the heavy side, but no discrete satellite components. In heavy metal (Ag+ or Hg++)-Cs2SO4 gradients, 4-8 satellite bands were revealed, comprising 5-9% of the total DNA. Purification of the satellites and recentrifugation in neutral CsCl demonstrated that 80-90% of this DNA would band in the shoulder, with the remainder in the main band. These satellites can account at most for 30% of the heavy shoulder DNA, thus most of the heavy shoulder DNA must be of lower repetition frequencies. Reassociation analyses of chicken DNA demonstrated that the complexity of the non-repetitive DNA is 9.49 X 10(8) nucleotide pairs, equivalent to about 90% of the haploid genome. Repetitive DNA comprises only 8-10% of the genome and has the following composition, relative to total DNA: 3.7% intermediate repetitive, 1.9% highly repetitive, and 3.9% "zero-time binding" DNA. This unusually low repetitive DNA content may be related to the small genome size of chickens, relative to other vertebrates, and to the presence of many microchromosomes in the chicken karyotype. Total cell RNA extracted from perfusion myoblasts, post-fusion myotubes, and myoblasts grown in BrdU was incubated in large excess with 3H-TdR labelled non-repetitive DNA and the resulting hybrids assayed by HAP chromatography. The amount of non-repetitive DNA represented in the RNA was found to increase from 7-8% in the myoblast stage to 10-11% in myotubes. An even smaller proportion, about 5%, is represented in the RNA of myoblasts prevented from differentiating by growth in BrdU.
The mechanism of the biosynthesis of albumin was studied in cell suspensions from rat liver. The cells were prepared by continuous perfusion of the liver in situ with 0.05% collagenase and 0.10% hyaluronidase and incubated under conditions optimized for the incorporation of amino acids into protein. Seven minutes after starting the incubation L-[1-14C]leucine was added, followed after 25 min by a 15 or 30-min chase with an 830-fold excess of non-radioactive L-leucine. Total protein, an albumin-like protein, and albumin were isolated from samples withdrawn immediately of total protein was found to remain constant after addition of the non-radioactive L-leucine, whereas that of the albumin-like protein decreased and that of albumin increased with incubation time. The increase in albumin radioactivity accounted for the decrease in radioactivity of the albumin-like protein, suggesting that the latter is a precursor of albumin. The precursor protein differed from albumin by an oligopeptide extension at the N-terminal end.
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The mechanism of albumin biosynthesis was studied in Morris hepatoma 5123tc in vivo and in hepatoma cell suspensions obtained by solubilizing the intercellular matrix with collagenase and hyaluronidase. In the in vivo experiments, L-[-14C]leucine was injected i.v. into rats bearing hepatomas in the muscles of both hind legs. After 14 min, tumors were removed and homogenized. A protein fraction quantitatively precipitable with antialbumin was isolated from the homogenate by acetone fractionation and precipitation with antiserum against serum albumin. This protein fraction was not homogeneous. With the use of 3 consecutive chromatographies on diethylaminoethyl cellulose, a very highly radioactive albumin-like protein could be separated from a large amount of only slightly radioactive albumin. In hepatoma cell suspensions incubated with L-[1-14C]leucine followed by a chase with excess nonradioactive L-leucine, radioactivity was incorporated first into the albumin-like protein and transferred thereafter into albumin, suggesting that albumin was synthesized via the albuminlike protein as precursor. In vivo, 1.8% of newly synthesized hepatoma protein was albumin or its precursor, compared with 1.2% in cell suspensions.
The effects of three oral doses of bedtime triazolam (0.25 mg, 0.5 mg, and 1.0 mg) a new benzodiazepine, on the laboratory sleep of insomniacs were studied in a double blind design which used the following 14 consecutive night schedule: 1-4 placebo; 5-11 drug; 12-14 placebo. Effects on sleep were measured objectively by conventional EEG/EOG/EMG sleep recordings and subjectively by questionnaires administered each morning. Side or toxic effects were assessed by screening physicals and questionnaires administered each morning and each evening and by a comparison of the prestudy vs. end-study physical exams and clinical lab tests. At the 0.5 mg dose triazolam significantly reduced several objective and subjective measures of insomnia. It had lesser effects at the 0.25 mg dose and equal or greater effects at 1.0 mg dose. There were no remarkable side or toxic effects at any dose.