Auto-radiographic determination of S35 in tissues after injection of methionine-S35 and sodium sulfate-S35

The loss of "bound" S(35) that occurs during various mounting procedures used in autoradiography was studied in healing surface wounds of rats treated with either methionine-S(35) or Na(2)S(35)O(4). Valid autoradiography of bound S(35) in this tissue is not possible until 48 hours after radiosulfate and 24 hours after radiomethionine injection, when the S(35) is almost entirely bound in large protein and polysaccharide molecules. Autoradiograms of S(35) given in both the organic and inorganic form reveal substantial over-all loss of the bound isotope from sections subjected to contact with solvents prior to autoradiography. A comparison of autoradiograms prepared by dry-mounting sections of frozen-dried tissue with autoradiograms of wet-mounted sections of the same tissue suggest that the loss is proportional to the extent of the contact with solvents. Evidence suggests that loss of the isotope occurs during contact of the ribbon or section itself with solutions after fixation and cutting and prior to radiation exposure. No appreciable loss of the bound isotope seems to occur during contact of the intact tissue specimen with a variety of fluid fixatives except for a marginal zone at the excision edges of the tissue. The potential hazard of displacement of the isotope during fixation, however, remains. Technics which prevent loss of the isotope and fogging of the nuclear emulsion permit the use of thinner sections and emulsion films and the fine resolution of image rendered possible by the physical properties of S(35).     

AUTORADIOGRAPHIC DETERMINATION OF S35 IN TISSUES AFTER INJECTION OF METHIONINE-S35 AND SODIUM SULFATE-S35

The loss of "bound" S³⁵ that occurs during various mounting procedures used in autoradiography was studied in healing surface wounds of rats treated with either methionine-S³⁵ or Na₂S³⁵O₄. Valid autoradiography of bound S³⁵ in this tissue is not possible until 48 hours after radiosulfate and 24 hours after radiomethionine injection, when the S³⁵ is almost entirely bound in large protein and polysaccharide molecules. Autoradiograms of S³⁵ given in both the organic and inorganic form reveal substantial over-all loss of the bound isotope from sections subjected to contact with solvents prior to autoradiography. A comparison of autoradiograms prepared by dry-mounting sections of frozen-dried tissue with autoradiograms of wet-mounted sections of the same tissue suggest that the loss is proportional to the extent of the contact with solvents. Evidence suggests that loss of the isotope occurs during contact of the ribbon or section itself with solutions after fixation and cutting and prior to radiation exposure. No appreciable loss of the bound isotope seems to occur during contact of the intact tissue specimen with a variety of fluid fixatives except for a marginal zone at the excision edges of the tissue. The potential hazard of displacement of the isotope during fixation, however, remains. Technics which prevent loss of the isotope and fogging of the nuclear emulsion permit the use of thinner sections and emulsion films and the fine resolution of image rendered possible by the physical properties of S³⁵.     

Subcellular distribution of 35S-sulfur in spinach leaves after application of 35SO 4 2- , 35SO 3 2- , and 35SO2

³⁵SO₂, ³⁵SO ₃ ^2- , and ³⁵SO ₄ ^2- , respectively, were applied to leaves of Spinacia oleracea L. for 60 min in the light. Thereafter, the specific activity was determined in the organelles separated by means of sucrose density gradient centrifugation. In mitochondria and peroxisomes, the specific activity was equally distributed in their protein moieties. After application of ³⁵SO₂ or ³⁵SO ₃ ^2- , the chloroplast lamellae are characterized by elevated specific activity, which is not found after application of ³⁵SO ₄ ^2- . Chloroplast stroma shows a low specific incorporation rate after application of either compound, which may be due to the low turnover rate of Fraction I protein.     

35 years of resistance

The misuse of antibiotics is not only a medical problem, but also a major agricultural one. The US Food and Drug Administration has recently shifted its focus to voluntary oversight.