Full text loading...
Chapter 11 : Metabolite Uptake by Active Transport, 1925 to 2000
This chapter deals with the kind of transport which is activated by metabolic energy, with solutes crossing membranes against their own gradient of electrochemical potential. In the 1940-50s, evidence of active transport of ions, amino acids, and glycosides was also reported for bacteria and for human erythrocytes. 2,4-dinitrophenol (DNP) inhibits active transport as it uncouples oxidative phosphorylation, mediating proton conductance across the inner membrane of the mitochondria. By the mid-1970s, proton symport was established as a means by which some substrates enter certain bacteria. Indeed, the concentration of certain amino acids and sugars by various mammalian and bacterial cells had been shown to depend on the coupling of transport to the flow of specifications, such as Na+, K+, or H+. Although most of the research on metabolite transport into yeasts has been done with saccharomyces cerevisiae, there has been a good deal of work on transport into several other species, especially during the 1970-80s. A glucose-repressible carrier was described in 1975 for K. lactis as taking up succinate, L-malate, fumarate, and 2-oxoglutarate by active transport. The occurrence of active transport of solutes into cells, with the energy being supplied by metabolism, was established in the 1930s by work on plant roots. At about the same time, the concentration of solutes by animal cells was also observed. However, biochemists generally failed to think of transport as a metabolic activity until Jacques Monod and his colleagues laid the foundations of membrane transport as an important part of metabolic studies in the 1950s.