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951.
Normal human red cells which have had their intracellular sodium (Nac) reduced have a diminished Na-K pump rate, but only if intracellular potassium (Kc) is high. If most of the Kc is replaced by tetramethylammonium or choline, both ouabain-sensitive Na efflux and K influx are significantly increased even with Nac below normal. Cells with reduced Nac and high Kc have an unchanged Na efflux if external potassium (Kext) is removed. In contrast, low-Na, low-K cells have a large ouabain-sensitive Na efflux which shows a normal response to removal of Kext. Neither low-K nor high-K cells have an altered ouabain-sensitive K efflux. Measurement at constant low Nac and varying Kc shows the pump Na efflux to be an inverse function of Kc. Thus, in low-Na cells, Kc appears to act as an inhibitor of the pump. Inhibition by high Kc can be seen even when Nac is normal. The effects attributed to Kc are distinguished experimentally from other variables such as cell volume, adenosine triphosphate concentration, effects of the replacement cations, and the method used to alter intracellular cation concentrations. A role is proposed for Kc, in cooperation with Nac, in regulating the pump rate of normal human red cells. 相似文献
952.
Betaine-Homocysteine Transmethylase in Pseudomonas denitrificans, a Vitamin B12 Overproducer 总被引:2,自引:1,他引:1 下载免费PDF全文
A pantothenate-methionine auxotroph (J741) of Pseudomonas denitrificans was isolated whose growth requirement for methionine could not be satisfied by known precursors of the amino acid, including homocysteine. However, some "methyl rich" compounds such as betaine and dimethylacetothetin (DMT) could satisfy the requirement. S-Methyl-methionine and S-adenosylmethionine were ineffective. Extracts were found to contain an enzyme, betaine-homocysteine transmethylase (BHTase), that uses betaine or DMT as a methyl donor and homocysteine as an acceptor to produce methionine. Growth of J741 in methionine leads to a total repression of the BHTase, whereas the use of DMT leads to a three- to sixfold stimulation of enzyme synthesis compared to betaine-grown cells. The pantothenate requirement is unrelated to the methionine auxotrophy, since the growth of other single auxotrophic mutants as well as revertants of J741 still have their methionine requirement satisfied by betaine or DMT. Another methionine auxotroph that could not use betaine for growth was devoid of BHTase activity. 相似文献
953.
Cancer as one of the most important human diseases does not present as formidable a problem as infectious disease did a century ago. The diversified cancer program, combining voluntary and governmental agencies in support of research, education and coordinated teamwork in the clinical care of the patient, presents a varied although unified approach to the problem that has never before been available for the study of any single human disease. Pathology, with its applied methods from the basic sciences, has a singular role in the scientific aspect of the cancer program. Representing a new specialty in medicine and embodying an inquiring approach to the study of human disease, pathology has a leading role to play. The pathologist, assuming the new role of “pathologist-physician” brings to the clinical care of the cancer patient the most precise methods of cancer diagnosis. The “pathologist-physician” should be a pivotal member of the “clinical team” in the immediate diagnosis, care and treatment of the cancer patient. 相似文献
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Louis F. X. Wilhelm 《The Western journal of medicine》1928,29(6):381-384