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Biomedical subjects

M M Salpeter

Publications and source records attributed to M M Salpeter.

At least 91 records · Page 5Linked to original sources
PubMed1974

The labeling of cultured cells of Acer with (14C)proline and its significance.

The distribution of the radioactivity from [(14)C]proline that is bound in cultured cells of Acer has been determined by electron microscope autoradiography. In this way proline may be related to the cell wall as a morphological entity rather than as a fraction in a biochemical separation of a heterogeneous crop of cells. The cells in culture may vary greatly. Some are active growing, turgid cells, with thin protoplasts tightly pressed against their walls; in others the protoplasts may spontaneously withdraw from the wall; in still others the protoplasts disorganize, and walls thicken and become sculptured as the cells differentiate and even senesce. Different culturing practices may affect the status of the cells, and this, in turn, affects the distribution of radioactivity from proline in the cells. Cells which are actively growing, turgid, and nucleated have the highest grain density in their protoplasts and nuclei; as the protoplasts of such cells withdraw from their walls, they retain the bulk of the radioactivity. On the other hand, in cells which have thickened walls and sparse protoplast contents, the radioactivity is accumulated in their walls. A high content of proline and hydroxyproline-rich protein is, therefore, not a necessary or invariable feature of the cell walls of cultured Acer cells but depends on the state of development of these cells.

Carbon Radioisotopes↗
PubMed1971

Resolution in electron microscope radioautography. II. Carbon 14.

Experimental resolution values, half distances (HD), were determined for electron microscope radioautography with (14)C as the source of radioactivity. These were about a factor of 1.5-2 times higher than for tritium. Grain distributions normalized in units of HD were found to fit the "universal" curves previously obtained for tritium.

Autoradiography↗
PubMed1970

Promitochondria of anaerobically grown yeast. IV. Conversion into respiring mitochondria.

Promitochondria of anaerobically grown Saccharomyces cerevisiae were selectively labeled in vivo by incubating the cells with [(3)H]leucine and cycloheximide. When the labeled cells were washed free of cycloheximide and adapted to oxygen in the presence of unlabeled leucine, the respiring mitochondria formed during adaptation proved to be radioactive. In contrast, only insignificant label was found in iso-1-cytochrome c which is synthesized de novo during adaptation. Respiratory adaptation of anaerobically grown yeast thus involves differentiation of promitochondrial organelles.

Adenosine Triphosphatases↗
PubMed1970

Glutamate uptake by a stimulated insect nerve muscle preparation.

Recent reports suggest that glutamate may be the excitatory neuromuscular transmitter in insects. In this study, glutamate uptake by isolated cockroach nerve muscle preparations was investigated by means of chemical and electron microscope radioautographic techniques. We found that the preparation had a high affinity for glutamate and that nerve stimulation enhanced glutamate uptake. Chemical studies showed that the average tissue concentration of glutamate bound during a 1 hr incubation period in 10(-5)M glutamate-(3)H after nerve stimulation was 2.8 x 10(-5)M. Less than 1% of the radioactivity was present in the perchloric acid-precipitated protein fraction. Using electron microscope radioautography, we observed that sheath cells showed the highest glutamate concentration of all cellular compartments. Uptake was greater at neuromuscular junctions than in other regions of the tissue. The data suggest a possible mechanism for transmitter inactivation and protection of synapses from high blood glutamate.

Amino Acids↗
PubMed1969

Resolution in electron microscope radioautography.

An analysis of grain distributions around a radioactive line source (consisting of polystyrene-(3)H) showed that the shape of the distribution was independent of the factors that influence resolution, i.e. section and emulsion thickness, silver halide crystal, and developed grain size. These factors did effect the spread of the distribution, however, and thus the distance from the line source within which 50% of the total developed grains fell. We called this distance "half distance" (HD) and determined it for a variety of specimens. When grain distributions were normalized in units of HD, one could plot universal grain distributions for specimens with radioactive sources of various shapes. The use of HD and the universal curves in interpreting radioautograms is discussed.

Autoradiography↗
PubMed1969

Quantitative studies on enzymes in structures in striated muscles by labeled inhibitor methods. I. The number of acetylcholinesterase molecules and of other DFP-reactive sites at motor endplates, measured by radioautography.

Di-isopropylfluorophosphate (DFP) labeled with phosphorus-32 was applied to fragments of the diaphragm and sternomastoid muscles of the mouse, in conditions in which it saturated all available sites at the motor endplates. After adequate washing and exchange with unlabeled DFP, single endplates were obtained by microdissection and their radioactivity was found by beta track radioautography. The number of sites phosphorylated by DFP-(32)P per endplate was relatively constant for each muscle: in the sternomastoid, about 9 x 10(7) sites per endplate, in the diaphragm, about 3 x 10(7). Reaction with DFP-(32)P was abolished by prior treatment with unlabeled DFP. Labeling was unaffected by prior fixation in formaldehyde, but was inversely proportional to the time of incubation in the Koelle staining medium, when this preceded labeling. The contribution of acetylcholinesterase (AChase) to this total number of DFP-reactive sites was determined by three methods. The first involved reactivation of the phosphorylated AChase by pyridine-2-aldoxime methiodide (2-PAM), in conditions in which the reactivation of other enzymes would be insignificant. The other two methods involved protection of the active centers of AChase from phosphorylation by labeled DFP by use of 284C51, an inhibitor highly specific for this enzyme, or by use of eserine. Each of these methods indicated that about 35% of the DFP-reactive sites at endplates of the sternomastoid and diaphragm are AChase. The mean number of AChase molecules was thus found to be 3.1 x 10(7) and 1.1 x 10(7)per endplate in sternomastoid and diaphragm, respectively. No significant reaction of labeled DFP with muscle and nerve was observed. Mast cells in the muscle had a concentration of DFP-reactive sites far higher than the endplates.

Acetylcholinesterase↗
PubMed1969

Electron microscope radioautography as a quantitative tool in enzyme cytochemistry. II. The distribution of DFP-reactive sties at motor endplates of a vertebrate twitch muscle.

The distribution of diisopropylfluorophosphate (DFP)-sensitive enzyme sites at the neuromuscular junction was determined quantitatively by electron microscope radioautography after incubation of muscle fragments in DFP-(3)H. Most of the sensitive sites were located in the subneural apparatus at a concentration of 90,000 sites per micro(3) of cleft tissue or 12,000 sites per micro(2) of postjunctional membrane surface area. A considerable concentration is also present in the teloglial cap. It has previously been demonstrated (Rogers et al., 1966) that one-third of the DFP-sensitive sites at the endplate can be reactivated by pyridine-2-aldoxime methiodide (2-PAM)-a compound which selectively reactivates phosphorylated acetylcholinesterase. In the present study, it was found that this ratio of 1:2 holds also on a fine-structural level. Muscle mast cells were found to have a heavy concentration of bound DFP.

Acetylcholinesterase↗