OSMOADAPTACJA I SYSTEMY TRANSPORTU POTASU W BAKTERIACH GRAM-UJEMNYCH
1. Wstęp. 2. Systemy transportu K+ do komórki bakteryjnej. 2.1. System Trk. 2.2. System Ktr. 2.3. System Kdp. 2.4. System Kup. 3. Systemy wypływu K+ z komórki bakteryjnej. 4. Regulacja systemów transportu K+ do komórki bakteryjnej. 4.1. Kontrola systemów transportu K+ na poziomie ich aktywności. 4.2. Osmotyczna regulacja transportera Kdp na poziomie transkrypcji. 5. Podsumowanie
Abstract: Potassium (K+) is the major intracellular cation in bacterial cells. It plays a key role in maintaining the cell turgor, pH, adaptation to osmotic conditions, enzyme activation, and gene expression. The intracellular concentration of K+ is generally much higher than that in a growth medium and bacteria use a number of transporters and efflux pumps to maintain respective K+ concentration in cytoplasm. The best characterized K+ uptake systems in Gram-negative bacteria are: Trk, Kup, Ktr, and Kdp. Under hyperosmotic stress, in potassium-replete media at neutral and alkaline pH, the Trk system is the main K+ importer. It is a low – affinity, multiunit protein complex encoded by constitutively expressed genes that are. Under acidic conditions, when the activity of Trk is insufficient, a single component, i.e. the constitutive Kup transporter, with the affinity for K+ similar to that of the Trk system, is thought to be important. The Ktr transporter, resembling that of the Trk system, is composed of a membrane-spanning protein and a peripheral membrane-associated nucleotide – binding subunit. The Kdp-ATPase is a high affinity K+ uptake system that is expressed at very low potassium concentrations in the environment and in response to a decrease in cell turgor. Turgor, which is a signal and end the resulte of K+ import, is involved not only in the regulation of the Kdp transporter expression but also in the control of the activity of potassium uptake systems.
1. Introduction. 2. K+ uptake systems in bacterial cells. 2.1. Trk system. 2.2. Ktr system. 2.3. Kdp system. 2.4. Kup system. 3. K+ efflux systems in bacterial cells. 4. Regulation of K+ uptake systems. 4.1. Control of K+ uptake system activities. 4.2. Osmotic regulation of Kdp expression. 5. Summary