This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Sirotnak, F. M. Articles by Hutchison, D. J. Search for Related Content PubMed PubMed Citation Articles by Sirotnak, F. M. Articles by Hutchison, D. J.

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

Division of Experimental Chemotherapy, Sloan-Kettering Institute for Cancer Research, Cornell University Medical College, New York
Sloan-Kettering Division, Graduate School of Medical Sciences, Cornell University Medical College, New York

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 K_m of 0.9 x 10^–6M and a V_max of 1.9 x 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 x 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.