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Biomedical subjects

M Marcus

Publications and source records attributed to M Marcus.

At least 181 records · Page 10Linked to original sources
PubMed1976

Stability of vitamin B12 in the presence of ascorbic acid.

Experiments were performed in two independent laboratories, each using their own meal preparations which were exactly similar in composition to the meals described by Herbert and Jacob (J. Am. Med. Assoc. 230:241, 1974), in order to check their report that incubating meals (portions of daily food intake by man) of "modest" or "high" vitamin B12 content with increasing levels of added L-ascorbic acid (vitamin C) produced increasing destruction of vitamin B12. The present studies were performed with standardized and official methods. Vitamin B12 was determined microbiologically and by radioassay method. The results showed that 1) the vitamin B12 contents of these meals were in general agreement with values calculated from the literature for the foods involved, 2) the values obtained were manyfold higher than those reported by Herbert and Jacob, and 3) there was no deleterious effect of added ascorbic acid on the vitamin B12 content of meals, contrary to their published results.

Ascorbic Acid↗
PubMed1976

Effect of growth conditions on glutamate transport in the wild-type strain and glutamate-utilizing mutants of Escherichia coli.

The effects of growth conditions on the glutamate transport activity of intact cells and membrane vesicles and on the levels of glutamate-binding protein in wild-type Escherichia coli K-12 CS101 and in two glutamate-utilizing mutants, CS7 and CS2TC, were studied. Growth of CS101 on aspartate as the sole source of carbon or nitrogen resulted in a severalfold increase in glutamate transport activity of intact cells and membrane preparations to levels characteristic of the operator-constitutive mutant CS7. The high glutamate transport activity of mutant CS7 was not depressed further by growth on aspartate. Synthesis of glutamate-binding protein was not enhanced by aspartate in either strain. Mutant CS2TC produces a heat-labile repressor of glutamate permease synthesis and is therefore able to grow on glutamate at 42 C but not at 30 C. CS2TC cells grown in a glycerol-minimal medium at the restrictive temperature (30 C) exhibit low glutamate transport activity. Growth on aspartate at 30 C results in derepressed synthesis of glutamate permease. Cells grown on glycerol at 42 C have high glutamate transport activity. No further derepression is obtained upon growth on aspartate. Growth of CS101 and CS7 in "rich broth" greatly reduces the levels of glutamate-binding protein but does not appreciably affect glutamate transport by whole cells or membrane preparations. The identity of the carrier and the role of the binding protein in glutamate transport are discussed in the light of these findings.

Aspartic Acid↗
PubMed1976

Glutamate transport in membrane vesicles of the wild-type strain and glutamate-utilizing mutants of Escherichia coli.

A highly specific energy-dependent glutamate transport system was demonstrated in membrane vesicles of glutamate-utilizing Escherichia coli K-12 mutants. The glutamate transport activity of membranes from the parent strain, unable to grow on glutamate, was very low. With ascorbate-phenazine methosulfate as the electron donor, mutant preparations displayed 17 to 20 times higher activity than did the wild type. However, the affinity of the mutant carrier for L-glutamate remained the same as in the parent strain. Comparative inhibition analysis of glutamate transport in whole cells and membrane vesicles and of in vitro binding of glutamate to a specific periplasmic-binding protein suggests that under certain conditions the latter may be a component of the E. coli K-12 glutamate transport system.

Amino Acids↗
PubMed1976

Type B and non-B viral hepatitis in Jerusalem.

In a two-year survey of adult patients hospitalized with acute viral hepatitis in Jerusalem, 27% were reactive for the hepatitis B surface antigen (HB(s)Ag) by radioimmunoassay and therefore diagnosed as having hepatitis B. The majority of patients (73%) were non-reactive for HB(s)Ag and their diagnosis was non-B hepatitis ("type unspecifiable"). Thirty-one per cent of patients with hepatitis B and only 5% of patients with non-B hepatitis had histories consistent with parenteral transmission of hepatitis by blood transfusion or drug use. An additional 19% of the patients with hepatitis B had possible parenteral exposure and 50% had no obvious parenteral exposure, indicating that non-parenteral transmission of the hepatitis B virus (HBV) may be a significant epidemiological factor (50-69%) in the Jerusalem area. The prominent role of non-parenteral transmission of HBV is further evidenced by the relatively high prevalences of HB(s)Ag (0.97%) and antibody to hepatitis B surface antigen (anti-HB(s)) (19.0%) in healthy blood donors. These findings are consistent with the view that personal contact and intra-familial spread may be important factors in the epidemiology of HBV and indicate that non-parenterally transmitted HBV contributes significantly to endemic viral hepatitis in the Jerusalem area.

Acute Disease↗
PubMed1975

Micro-scale blood lead determinations in screening: evaluation of factors affecting results.

The Delves micro-scale technique for blood lead analysis is an accurate method for screening capillary blood specimens, obtained by fingerstick, for lead intoxication. Results are affected by the age of cup, loop, and hollow-cathode tube and by the spatial relationship between optical tube and cup. Because the glass in many commercially available capillary tubes (used in specimen collection) contains lead and cannot be decontaminated, a lead-free glass tube must be used. A solution of citric acid in ethanol (20 g/liter) effectively cleanses the puncture site. A double-blind study of 207 specimens gave a mean value of 276.6 plus or minus 105.8 mug/liter (1SD) for the micro-scale method vs. 273.2 plus or minus 99.0 for a macro-scale method. The mean coefficent of variation for the micro-scale method was 5.75 percent plus or minus 1.9 (SD). We conclude that values of 480 mug/liter or below are not "toxic" (i.e., are significantly less than 600 mug/liter, the value at which therapy is begun). The method is shown to be satisfactory as a screening procedure and for confirming lead analyses done by other methods.

Adult↗
PubMed1974

Bacillus subtilis DNA polymerase III is required for the replication of the virulent bacteriophage phi e.

The virulent phage phie of Bacillus subtilis which contains hydroxymethyluracil in its DNA requires host DNA polymerase III for its DNA replication. DNA polymerase III(ts) mutant cells infected with phie at restrictive temperatures do not support phage DNA synthesis. However, phie grows normally both at low and high temperatures in the mutant's parent strain and in spontaneous DNA polymerase III(+) revertants isolated from the mutant strain. Temperature-shift-down experiments with phie-infected cells having thermosensitive DNA polymerase III (pol III(ts)) indicate that at 48 C the thermolabile DNA polymerase III is irreversibly inactivated and has to be synthesized de novo after the shift to 37 C, before phage DNA synthesis can begin. Temperature-shift-up experiments with phie-infected mutant cells show that phage replication is arrested immediately after the temperature shift and indicate that phie requires DNA polymerase III throughout its replication stage.

Bacillus subtilis↗