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S R Dickman

Publications and source records attributed to S R Dickman.

15 recordsLinked to original sources
PubMed1980

Effects of potassium chloride concentration on protein content and polyphenylalanine synthesizing capability of 40S ribosomal subunits from canine pancreas.

Ribosomal small subunits from canine pancreas were used to survey the effects of potassium chloride in the concentration range from 0.4 to 1.25 M. When combined with 60S particles, the treated 40S subunits showed no significant change in phenylalanine incorporating activity until exposure to 0.95 M KCl. Decreases in protein content of the subunits were observed at high ionic strengths. Attempts to separate dissociated ribosomal protein and the remaining core particles treated with 1.25 M KCl by centrifugation of the salt-treated particles though a 40% sucrose cushion led to the observation that ribosomal subparticles isolated in this manner retained full phenylalanine incorporating activity, whereas centrifugation through other solutions resulted in inactive or less active particles. Experiments were performed to elucidate the mechanism by which the 40% sucrose cushion was stabilizing the high salt treated 40S subunits. Two-dimensional gel electrophoresis of the proteins of the various particles isolated in the study was performed. The active 40S particles contained 23-31 protein spots. The isolation of fully active 40S subunits with fewer proteins than previously reported should simplify elucidating their role in the function of the small subunit.

Animals↗
PubMed1977

Ribonucleotide reduction and the possible role of cobalamin in evolution.

The biological pathways of ribonucleotide reduction are briefly reviewed. The hypothesis is presented that reduction of ribonucleoside triphosphates to their deoxynucleotide analogs through the mediation of vitamin B12 or a similar corrinoid preceded and was necessary for the subsequent development of a DNA-type genome. There are two known biological systems for ribonucleotide reduction: (1) The ribonucleoside diphosphate reduction system which utilizes a nonheme iron ribonucleotide reductase enzyme, thioredoxin and its reductase, and NADPH. This enzyme complex is found in most bacteria, some higher organisms, and in all animals. (2) The ribonucleoside triphosphate reduction system which utilizes adenosyl cobalamin, ribonucleotide reductase and either thioredoxin or a disulfhydryl compound. The cobalamin-dependent reductase is restricted to a few species of bacteria and blue-gree algae. This system is considered more primitive than the iron reductase one based on their differences in distribution, components, and products.

Bacteria↗
PubMed1976

Catalytic activation of transfer ribonucleic acid by a mammalian protein.

A tRNA activator has been isolated from mammalian organs which increases the capability of tRNA to accept certain amino acids through the action of mammalian aminoacyl-tRNA synthetases. This activity may be separated from the aminoacyl-tRNA synthetases for isoleucine, lysine, serine, and methionine by fractionation of liver or pancreas cytosol with ammonium sulfate or by chromatography over Sephadex G-200. The tRNA activating material is nondialyzable and is destroyed by trypsin or short heating. It acts catalytically. A molecular weight of approximately 45,000 was obtained by chromatography of tRNA activator on a calibrated Sephadex G-150 column. Activator increases acceptance of yeast tRNA for the amino acids isoleucine, leucine, lysine, serine, and methionine. It shows higher activity on liver tRNAMet f, tRNAMet m, and tRNALys than on unfractionated liver tRNA. Removal of protein from mammalian tRNA by extra phenol extractions, chromatography, or proteinase treatment increases its response to activator.

Amino Acids↗
PubMed1966

Effects of pancreozymin, urecholine and actinomycin D on the metabolism of ribonucleic acid by canine pancreas.

1. Canine pancreas slices were incubated with [6-(14)C]orotic acid and the rate of its incorporation into RNA was measured. RNA was fractionated by shaking homogenates with phenol at 2 degrees , 50 degrees , 65 degrees and 80 degrees . Cytoplasmic RNA was extracted at the lowest temperature and nuclear RNA at the higher temperatures. The samples were centrifuged through sucrose gradients and the E(260) and (14)C-sedimentation patterns determined. Incorporation of orotic acid was very rapid into cytoplasmic 4s RNA. This probably represents end-group turnover. No incorporation into cytoplasmic ribosomal RNA was observed. 2. The nuclear 50 degrees -RNA exhibited two E(260) peaks, at 18s and 28s. This portion of the sample contained but moderate amounts of [(14)C]RNA. The highly labelled material had sedimentation coefficients in the range 35-50s. The nuclear 65 degrees -RNA showed an E(260) peak at 16s. The [(14)C]RNA peak occurred at 25-35s and this portion demonstrated the highest specific activity of any RNA fraction. 3. The 50 degrees -RNA, 65 degrees -RNA and 80 degrees -RNA were hydrolysed and their base compositions were determined. All three samples possess a ribosomal type of composition (G+C)/(A+U)=(1.4-1.7). For this reason they are considered to contain ribosomal precursor RNA as their major constituent. 4. Actinomycin D (0.5mug./ml.) in the incubation medium inhibited incorporation of orotic acid into both nuclear fractions but not into 4s RNA. 5. The cholinergic drug Urecholine inhibited incorporation into the heavy, high-specific-activity portions of the nuclear fractions but did not inhibit incorporation into the ribosomal precursor type of nuclear RNA. A similar result was also obtained with the hormone pancreozymin. Moderate inhibition of incorporation of orotic acid into 4s RNA likewise resulted from the presence of the drug and the hormone.

Animals↗