Genetically Alterable Transport of Amethopterin in Diplococcus pneumoniae I. Physiological Properties and Kinetics of the Wild-type System
AUTOR(ES)
Sirotnak, Francis M.
RESUMO
A system of H3-amethopterin uptake, physiologically and kinetically resembling active transport, has been described in Diplococcus pneumoniae. Uptake by this system has a pH optimum near 6.0, is temperature-dependent, requires a readily available source of energy, and conforms to Michaelis-Menten kinetics. The system showed a Km of 0.9 × 10−6m and a Vmax of 1.9 × 10−13 moles per min per mg (dry weight). Both folate and H2-folate compete with H3-amethopterin for the same system, but to a limited degree. The intracellular concentration of H3-amethopterin accumulated at equilibrium was 1.06 × 10−9 moles/ml or fivefold the external concentration when the latter was limiting, but at least 60-fold the internal concentration attained solely by diffusion in the same time interval at 0 C.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=315003Documentos Relacionados
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