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. 1967 Jan;93(1):309–314. doi: 10.1128/jb.93.1.309-314.1967

Genetically Alterable Transport of Amethopterin in Diplococcus pneumoniae I. Physiological Properties and Kinetics of the Wild-type System

Francis M Sirotnak 1,2, M Gay Sargent 1,2, Dorris J Hutchison 1,2
PMCID: PMC315003  PMID: 4381315

Abstract

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.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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