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C Long

Publications and source records attributed to C Long.

At least 127 records · Page 7Linked to original sources
PubMed1975

Adenine formation from adenosine by mycoplasmas: adenosine phosphorylase activity.

Mammalian cells have enzymes to convert adenosine to inosine by deamination and inosine to hypoxanthine by phosphorolysis, but they do not possess the enzymes necessary to form the free base, adenine, from adenosine. Mycoplasmas grown in broth or in cell cultures can produce adenine from adenosine. This activity was detected in a variety of mycoplasmatales, and the enzyme was shown to be adenosine phosphorylase. Adenosine formation from adenine and ribose 1-phosphate, the reverse reaction of adenine formation from adenosine, was also observed with the mycoplasma enzyme. Adenosine phosphorylase is apparently common to the mycoplasmatales but it is not universal, and the organisms can be divided into three groups on the basis of their use of adenosine as substrate. Thirteen of 16 Mycoplasma, Acholeplasma, and Siroplasma species tested exhibit adenosine phosphorylase activity. M. lipophilium differed from the other mycoplasmas and shared with mammalian cells the ability to convert adenosine to inosine by deamination. M. pneumoniae and the unclassified M. sp. 70-159 showed no reaction with adenosine. Adenosine phosphorylase activity offers an additional method for the detection of mycoplasma contamination of cells. The patterns of nucleoside metabolism will provide additional characteristics for identification of mycoplasmas and also may provide new insight into the classification of mycoplasmas.

Acholeplasma laidlawii↗
PubMed1974

The influx of calcium ions into human erythrocytes during cold storage. The influences of extracellular pH, intracellular adenosine triphosphate and efflux of univalent cations.

1. When human erythrocytes are stored at 3 degrees C for several days as a suspension in iso-osmotic sucrose or KCl, containing CaCl(2), the rates of cellular ATP degradation are similar. 2. During cold storage of erythrocytes in sucrose-CaCl(2) medium, Ca(2+) influx and univalent-cation efflux occur, the pH value of the suspending medium rises and the intracellular pH falls. These pH changes correlate reasonably well with alterations in the membrane potential calculated from Cl(-) distribution. 3. The presence of Ca(2+) in the medium does not increase the rate of univalent-cation efflux from the cells. 4. When the pH of the medium is raised by addition of buffers, the rates of both Ca(2+) influx and univalent-cation efflux increase. 5. Replacement of sucrose by KCl as the main osmotic component of the medium completely suppresses Ca(2+) influx and univalent-cation efflux, although the pH of the KCl medium is higher than that of the sucrose medium. 6. When sucrose is replaced by choline chloride, Ca(2+) influx and univalent-cation efflux still occur, and the pH of the medium is similar to that found in iso-osmotic KCl. 7. When valinomycin, Pb(2+) or Cd(2+) are added to the iso-osmotic sucrose medium, the rate of efflux of univalent cations increases as also does the influx of Ca(2+). 8. From these and other observations, it was concluded that it is univalent-cation efflux rather than ATP depletion or elevated extracellular pH which is the prerequisite for Ca(2+) influx during cold storage.

Adenosine Triphosphate↗
PubMed1973

The influx of calcium ions into human erythrocytes during cold storage.

1. When human erythrocytes, suspended in iso-osmotic sucrose containing CaCl(2), are stored at 3 degrees C, Ca(2+) influx into the cells occurs. Simultaneously, efflux of K(+), Na(+), Cl(-) and water takes place and cell volume diminishes. 2. The extent of Ca(2+) influx increases with duration of cold storage and with increasing concentration of Ca(2+) in the suspending medium. 3. Erythrocytes that have been thus loaded with Ca(2+) exhibit Ca(2+) efflux against a concentration gradient when subsequently incubated at 37 degrees C. 4. Ca(2+) influx likewise occurs when the sucrose of the medium is replaced by iso-osmotic solutions of other non-ionized compounds. 5. Replacement of sucrose by iso-osmotic KCl or NaCl greatly diminishes the rate of Ca(2+) influx during cold storage; however, in iso-osmotic choline chloride, Ca(2+) influx is as rapid as in sucrose. 6. Preincubation of erythrocytes in iso-osmotic sucrose at 37 degrees C causes rapid efflux of K(+) and Na(+) and renders the cell membranes highly permeable to Ca(2+) during subsequent cold storage. 7. Preincubation of erythrocytes in iso-osmotic NaCl at 37 degrees C with trypsin or neuraminidase is without effect on the permeability of the membrane towards Ca(2+). 8. The experimental results lead to the conclusion that the main prerequisite for Ca(2+) influx into erythrocytes is the partial depletion of the cells of their univalent cations.

Biological Transport↗