SUMMARY: Washed suspensions and cell-free extracts of grown on Lemco agar, to which intermediates of the tricarboxylic acid cycle had been added, were tested for their ability to oxidize succinate, fumarate, malate, pyruvate, acetate, α-oxoglutarate and citrate. Whole organisms had lag periods of 2-3 hr. before citrate was oxidized rapidly, except when citrate or acetate had been added to the growth medium. There were lag periods of about 10 min. before rapid and linear oxidation of succinate by organisms grown on acetate; of fumarate by organisms grown on acetate or pyruvate; and of acetate by organisms grown on malate, pyruvate, α-oxoglutarate, fumarate or succinate. There were no lags for malate, pyruvate or α-oxoglutarate by organisms grown on any of the substrates tested. Organisms grown on malonate or Lemco agar to which no additions had been made had lags for all the substrates. Glucose-grown organisms had lags for all the intermediates except succinate. Only malonate-grown organisms oxidized malonate rapidly and linearly, and organisms grown without malonate had lag periods of 2-3 hr. before oxidizing this substrate. Cell-free extracts from organisms with lag periods before the oxidation of citrate, acetate, fumarate, malate, succinate and α-oxoglutarate were shown to oxidize these substrates without a lag period. Pyruvate and malonate were not oxidized by any of the extracts including those from organisms grown on these substrates. Chloramphenicol inhibited the adaptation to substrates by whole organisms but was without effect on the oxidation by cell-free extracts. The significance of these findings in relation to the hypothesis of specific permeases for the transport of organic molecules into the cell is discussed.


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