Na(+)-dependent succinate uptake in Corynebacterium glutamicum.

Succinate is effectively taken up by washed cells of Corynebacterium glutamicum. The apparent Km value of uptake is about 150 microM and the Vmax 4-7 nmol (mg dry weight)-1 min-1 and uptake can be competetively inhibited by fumarate and oxaloacetate. The activation energy was determined to be 50 kJ/mol. The transport activity is clearly dependent on the presence of Na+ ions in the incubation medium and on the membrane potential and has a pH optimum around 8.5. It is concluded that succinate is taken up in C. glutamicum via a specific carrier by a secondary active, Na+ coupled mechanism.

Uptake of glutamate in Corynebacterium glutamicum. 1. Kinetic properties and regulation by internal pH and potassium.

The active uptake system for glutamate in Corynebacterium glutamicum is inducible by growth on glutamate as sole energy and carbon source and is also susceptible to catabolite repression by glucose. The basic level of uptake activity is low in glucose-grown cells (1.5 nmol.mg dry mass-1.min-1), it is intermediate when acetate is the carbon source (3.8 nmol.mg dry mass-1.min-1) and becomes fully induced by glutamate (15 nmol.mg dry mass-1.min-1). In all cases the uptake has, except for different Vmax values, identical kinetic and energetic properties, and is characterized by a low apparent Km value of 0.5-1.3 microM and by high substrate specificity. The transported substrate species is the deprotonated form which can also be concluded from the extremely high pH optimum of transport above pH 9. Glutamate uptake in cells grown in media with low K+ concentration is not influenced by external Na+ but is drastically stimulated by addition of K+. Stimulation by K+ could be separated into two different mechanisms. (a) Addition of K+ increases the internal pH, thereby stimulating glutamate uptake which is regulated by the internal pH in C. glutamicum. The apparent pK of the internal 'pH switch' is 6.6; below this value, uptake of glutamate is inhibited. (b) Internal K+ also directly promotes glutamate uptake. Effective uptake of glutamate can be observed only when the cytosolic K+ concentration exceeds a threshold value of about 200 mM. Stimulation of glutamate uptake by external K+ is not due to functional coupling of K+ and glutamate transport but reveals the necessity to replenish the internal K+ pool.

Transport of branched-chain amino acids in Corynebacterium glutamicum.

The transport of branched-chain amino acids was characterized in intact cells of Corynebacterium glutamicum ATCC 13032. Uptake and accumulation of these amino acids occur via a common specific carrier with slightly different affinities for each substrate (Km[Ile] = 5.4 microM, Km[Leu] = 9.0 microM, Km[Val] = 9.5 microM). The maximal uptake rates for all three substrates were very similar (0.94 - 1.30 nmol/mg dw.min). The optimum of amino acid uptake was at pH 8.5 and the activation energy was determined to be 80 kJ/mol. The transport activity showed a marked dependence on the presence of Na+ ions and on the membrane potential, but was independent of an existing proton gradient. It is concluded, that uptake of branched-chain amino acid transport proceeds via a secondary active Na+-coupled symport mechanism.

The simultaneous determination of carbon dioxide release and oxygen uptake in suspensions of plant leaf mitochondria oxidizing glycine.

The construction and operation of a device for continuous measurement of CO(2) release by suspensions of respiring mitochondria is described. A combination of this device with a Clark-type O(2) electrode was used for simultaneous measurement of respiration and of CO(2) release by spinach and pea leaf mitochondria with glycine as substrate. Both mitochondrial preparations showed high rates of respiration and high respiratory control ratios. The addition of oxaloacetate not only inhibited O(2) uptake substantially, but also greatly stimulated glycine oxidation as monitored by CO(2) release. In spinach leaf mitochondria, the maximal rates of glycine oxidation thus obtained, were two times higher than the rate of glycine oxidation required at average rates of photorespiration. It is concluded from these results that under saturating conditions the capacity of glycine oxidation by intact mitochondria exceeds the capacity of glycine-dependent respiration.