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Biomedical subjects

A Marcus

Publications and source records attributed to A Marcus.

At least 73 records · Page 4Linked to original sources
PubMed1983

De novo synthesis of 3'-nucleotidase in germinating wheat embryo.

The enzyme 3'-AMP nucleotidase was purified 2,500- to 5,000-fold from extracts of an acetone powder of wheat (Triticum aestivum) embryonic axes germinated for 40 hours. Sodium dodecyl sulfate acrylamide gel electrophoresis and chromatography on Biogel-P100 indicate that the enzyme is monomeric with a molecular weight of 39,000. Extracts of embryos germinated up to 6 hours have only 1% of the 40-hour level of enzyme activity. To see if the increase to 40 hours represents de novo synthesis, extracts were compared for their ability to react with a rabbit antibody prepared against the enzyme. In immunodiffusion tests, 40-hour extracts showed a strong precipitin line coincident with that of the purified enzyme, whereas no precipitation was observed with 1-hour extracts. When the enzyme present in 40-hour extracts was partially inactivated by EDTA, it still blocked the ability of the antibody to inhibit enzyme activity. Extracts of 1-hour embryos, in contrast, were not able to block the inhibitory activity of the antibody. Embryos allowed to take up (35)SO(4) between 40 and 46 hours of germination synthesized (35)S-labeled 3'-nucleotidase. In contrast, no radioactive protein synthesized by embryos during the first 6 hours of germination coincided on gel electrophoresis with the enzyme. These results indicate that the increase in 3'-nucleotidase activity is a consequence of de novo synthesis of the enzyme.

Journal Article↗
PubMed1983

Early growth of wheat embryonic axes and the synthesis of RNA and DNA.

The requirement for the synthesis of RNA and DNA in early germination of wheat (Triticum aestivum var Newana) embryonic axes has been studied by incubating embryos in the presence of appropriate inhibitors and monitoring both embryo growth and the rates of specific metabolic processes. Experiments with 5-fluorouridine showed that both rRNA and DNA synthesis could be curtailed by 60 to 70% without affecting embryo growth to 24 hours. Similarly, the presence of mitomycin C and methotrexate inhibited DNA synthesis 70%, with only a small effect on growth. Experiments with a range of concentrations of cordycepin and alpha-amanitin indicated that mRNA synthesis could be curtailed by 30 to 40% within the first 8 hours of germination with only a small effect on embryo growth. Thus, at least the initial phases of seed embryo germination are not closely linked to the synthesis of mRNA, rRNA, or DNA. Maximal sensitivity of embryo growth was obtained with cycloheximide and 2-(4-methyl-2,6-dinitroanilino)-N-methyl propionamide, supporting the idea that protein synthesis is the macromolecular process most closely linked to early germination.

Journal Article↗
PubMed1982

A heat-stable protein synthesis initiation factor from wheat germ.

A protein synthesis initiation factor of molecular weight 21,500 has been purified to homogeneity from extracts of wheat germ. The factor, referred to as D2d, is stable to heating for 5 min at 75 degrees C and loses less than 15% of its activity upon a similar treatment at 90 degrees C. In contrast, all other wheat germ protein synthesis factors are inactivated by heating for 5 min at 65 degrees C. Formation of 80 S ribosome . Met-tRNAiMet complexes from 40 S ribosome . Met-tRNAiMet complexes, as measured by the binding of [3H]Met-tRNAiMet, is almost completely dependent upon the presence of component D2d. The shift in sedimentation of the ribosome subunits to the 80 S ribosome region, however, occurs in the absence of factor D2d. Thus, the role of the factor is not to join the ribosomal subunits, but rather to keep the Met-tRNAiMet bound to the ribosome. The formation of 40 S ribosome . Met-tRNAiMet complexes is increased 2-fold by the presence of factor D2d. Fixing this complex with glutaraldehyde results in the binding of more Met-tRNAIMet than a nonfixed incubation in the presence of D2d. These results suggest that the primary interaction with the ribosomal subunit can occur in the absence of factor D2d, but that the presence of the factor stabilizes the ribosome-bound Met-tRNAiMet.

Hot Temperature↗
PubMed1982

Germination of wheat embryos and the transport of amino acids into a protein synthesis precursor pool.

Wheat (Triticum aestivum L. var. Lew) embryonic axes take up externally supplied radioactive amino acid (from a solution greater than 2 millimolar) such that the specific radioactivity of the total internal amino acid rapidly reaches that of the external solution. Nevertheless, incorporation of radioactive amino acid into protein increases steadily as the concentration of external amino acid is increased, indicating that the amino acid that is precursor to protein synthesis is not in equilibrium with the total internal amino acid pool. When the external source of amino acid is removed, incorporation of radiolabeled amino acid into protein continues at a rate comparable to that of embryos maintained in the radioactive solution. In explanation of these data, it is suggested that there are two separate cytoplasmic pools of amino acids, one a protein synthesis precursor pool, and the second, an expandable pool into which exogenous radioactive amino acids are taken up. The protein synthesis pool is fed at a limited rate from the expandable pool and at a far greater rate from an endogenous source. As a consequence, the specific activity of the amino acid that is the precursor for protein synthesis is considerably below that of the total internal pool and is determined by the rate of movement into the protein synthesis pool from the expanded radioactive cytoplasmic pool.The rate of movement of amino acids from the expandable pool into the protein synthesis pool increases approximately 5-fold during the initial 4.5 hours of embryo germination. When this change is considered in analyzing the relative rates of protein synthesis, there is probably no more than a 2-fold increase in protein synthetic capacity between embryos germinated for 1.5 and 4.5 hours. The leveling off of the change in transport capacity after 4.5 hours suggests that the earlier increase in the rate of this process may be a necessary step before the embryos can begin to accelerate their growth rate.

Journal Article↗
PubMed1981

Kaposi's sarcoma in homosexual men-a report of eight cases.

The clinical findings in eight young homosexual men in New York with Kaposi's sarcoma showed some unusual features. Unlike the form usually seen in North America and Europe, it affected younger men (4th decade rather than 7th decade); the skin lesions wee generalised rather than being predominantly in the lower limbs, and the disease was more aggressive (survival of less than 20 months rather 8-13 years). All eight had had a variety of sexually transmitted diseases. All those tested for cytomegalovirus antibodies and hepatitis B surface antigen of anti-hepatitis B antibody gave positive results. This unusual occurrence of Kaposi's sarcoma in a population much exposed to sexually transmissible diseases suggests that such exposure may play a role in its pathogenesis.

Adult↗
PubMed1980

In vivo synthesis of 6-azauridine 5'-triphosphate and incorporation of 6-azauridine into RNA of germinating wheat embryonic axes.

The cytostatic effect of 6-azauridine on cell growth is generally regarded to be a consequence of the inhibition of de novo pyrimidine biosynthesis by the metabolite, 6-azauridine 5'-monophosphate. We show here that wheat embryonic axes further metabolize 6-azauridine to the 5'-triphosphate and incorporate the analogue into RNA, thus offering an alternative mechanism for growth inhibition. At a level of 6-azauridine required to maximally inhibit UTP biosynthesis, the ratio of 6-azaUTP to UTP is about 2:1 and substitution of 6-azauridine for uridine in new RNA is on the order of 1 in 18. The new metabolites of 6-azauridine are identified by high pressure and thin layer chromatography coupled with enzyme treatments.

Azauridine↗
PubMed1980

RNA synthesis in germinating embryonic axes of soybean and wheat.

The rate of synthesis of RNA during early germination of wheat and soybean embryos was investigated by ascertaining the incorporation of radioactive uridine into RNA. In wheat embryos, where the lag period preceding rapid growth is 5.5 hours, there is a 2-fold increase in RNA synthesis between 1.5 and 5.5 hours, with half of the increase occurring by 3.5 hours. In soybean axes, where the lag period is 9.5 hours, the increased rate of RNA synthesis is 5.5-fold between 1.5 and 9.5 hours, with three fourths of this increase occurring after 4 hours.Analysis of the ratio of radioactivity incorporated into the 18S and 26S rRNAs of the germinating embryos provided a further measure of the increased rates of RNA synthesis. With wheat embryos, the 26S/18S ratio increased from 1.0 at 1.5 hours to 1.5 at 3.5 hours, while with the soybean axes, distinct ribosomal patterns were obtained only after 4 hours and the 26S/18S rRNA ratio increased from 0.4 at 4 hours to 1.0 at 9 hours. The extent of methylation of the rRNA synthesized at 4 and 9 hours in the soybean axes was similar, indicating that the methylating capacity of the axes is probably not rate limiting to rRNA synthesis. In both seed embryo systems the level of UTP increased 2 to 3-fold during the lag phase of germination. With wheat embryos, the time course of the increase in UTP correlated approximately with the change in the rate of RNA synthesis. With the soybean axes, however, the increase in the rate of RNA synthesis occurred predominantly after the rise in the level of UTP.

Journal Article↗
PubMed1979

RNA synthesis in growing and stationary cells of a culture of Scarlet Rose. Disproportionate synthesis of ribosomal subunits in the stationary state.

RNA synthesis has been investigated in resting and growing cells of a culture of Scarlet rose. The rates of messenger RNA (mRNA) and ribosomal RNA (rRNA) synthesis are five- and ten-fold higher, respectively, in the growing culture. In stationary phase cultures, newly synthesized 26S and 18S rRNA do not appear in the cytoplasm in equimolar amounts. Rather, the 26S/18S ratio of [3H]-uridine labeled rRNA of stationary cells ranged from 0.9 to 1.3 while the ratio of the corresponding fraction from growing cells was 1.6 to 2.0. A similar result was obtained when cells were labeled with [3H-CH3] methionine. Pulse chase experiments demonstrated that the nascent pre-rRNA in resting cells could be chased into polysomes. These data are interpreted to indicate that a major part of the regulation of rRNA synthesis in stationary cells is at the level of the processing of the rRNA transcript.

Cell Cycle↗
PubMed1979

Germination of soybean embryonic axes: nucleotide sugar metabolism and initiation of growth.

UDP-Sugars comprise the dominant class of nucleotide sugars in isolated soybean axes during early germination. While "dry" axes contain 1 nanomole per axis of UDP-sugars, further synthesis is initiated upon imbibition such that the concentration of total UDP-sugars reaches 8 nanomoles per axis or roughly 1 millimolar after 10 hours, when the axes begin to elongate. The GDP-sugars are essentially absent before imbibition, accumulate rapidly for 90 min to 173 picomoles per axis, then decrease somewhat, reattaining the earlier peak level shortly before growth begins. Meanwhile, the level of ADP-sugars is unchanged. These data indicate that the 10-hour lag period preceding axis growth does not result from a diminished ability to synthesize a major category of nucleotide sugars.Relative rates of synthesis of individual UDP- and GDP-sugars were determined by incorporation of [(3)H]uridine or [(3)H]guanosine. The distribution of label in the different classes of UDP-sugars and in the single class of GDP-sugar was quantitatively similar when analyzed before, at the onset, or during early growth. It therefore seems unlikely that synthesis of a key nucleotide sugar controls the initiation of growth.The possible relevance of nucleotide sugars to growth is discussed and new methods for enzymic analysis of picomole levels of nucleotide sugars are described.

Journal Article↗
PubMed1978

Preformed Messenger RNAs and Early Wheat Embryo Germination.

Wheat (Triticum aestivum L.) embryo homogenates have been fractionated into three cell fractions from which RNA was extracted and assayed for mRNA content by in vitro translation and by [(3)H]polyuridylic acid hybridization. In dry embryos the preformed mRNAs are distributed equally between a rapidly sedimenting "pellet" fraction and a cytoplasmic "ribosomal/subribosomal" fraction. During germination 25 to 40% of the total mRNA becomes polyribosomal. The remaining 60 to 75% is retained in the pellet and ribosomal/subribosomal fractions.To compare the nucleotide sequences of the different mRNA fractions, cDNAs were transcribed from polyribosomal (A+) RNA of 40-minute imbibed embryos and from total A(+) RNA of dry embryos, and the ability of these cDNAs to hybridize with the more prevalent classes of mRNA from the different cell fractions was analyzed. The results suggest that there is no significant difference between the preformed mRNAs that move into polyribosomes and those remaining in the nonpolyribosomal fractions. In addition there appears to be no difference between the mRNAs of polyribosomes from embryos germinated for 45 minutes and 5 hours. Between 5 hours and 2 days, however, there is a considerable change in the mRNA composition of the embryos. We conclude for the prevalent classes of message, that the preformed mRNAs of the wheat embryo are not involved in temporal regulation of early development but that they function primarily to allow a rapid resumption of growth upon exposure of the embryo to water.

Journal Article↗
PubMed1978

Transformation of monocytes into "fat" cells.

Human peripheral blood leukocytes, when cultured in soft agar give rise to giant (100 to 500 micrometer.) "foam cells." Investigation of the origin and properties of the cells proved that they were derived from monocytes in that the cells adherent to glass after 24 hours in culture were phagocytic, elaborated lysozyme and bore receptors for complement and immunoglobulin. The increment in size was accounted for primarily by large inclusions which on histochemical and biochemical analyses were shown to consist predominantly fo neutral fat. Transformation to fat cells took place in the absence of mitosis. Fc receptors were retained but complement receptors were lost. These observations suggest a role for monocytes in the replacement of hematopoietic tissue by fat in certain hypoplastic states. The cultured monocytes may also serve to facilitate the study of fat synthesis and metabolism in vitro.

Adipose Tissue↗