Cadmium-sensitive targets in the aerobic respiratory metabolism of Staphylococcus aureus.
Studies on the effect of various Cd2+ concentrations on substrate oxidation by whole cells of cadmium-sensitive Staphylococcus aureus 17810S showed that oxidation of glutamate or pyruvate was highly sensitive to low Cd2+ concentrations (5 microM), whereas L-lactate oxidation was insensitive even to high Cd2+ concentrations (100 microM). Location of the cadmium-sensitive targets in the enzyme systems involved in oxidation of these substrates was studied in subcellular fractions prepared from cells pretreated with 5 or 100 microM Cd2+. Activities of the cytoplasmic 2-oxoglutarate dehydrogenase complex (ODHC)') and pyruvate dehydrogenase complex (PDHC) were strongly inhibited with 5 microM Cd2+, while with 100 microM Cd2+ the inhibition was almost complete. In contrast, activities of the cytoplasmic NAD-dependent glutamate dehydrogenase (NAD-GDH), the membrane-bound NADH dehydrogenase (NDH) and HQNO-sensitive NADH oxidase were not sensitive to 100 microM Cd2+. These data indicate that the accessible, cadmium-sensitive targets are located only in the cytoplasmic ODHC and PDHC. It is postulated that two vicinal dithiols present in ODHC and PDHC may be regarded as the primary cadmium-sensitive targets in the systems oxidizing glutamate or pyruvate. Since activities of the membrane-bound NAD-independent L-lactate dehydrogenase (iLDH) and HQNO-sensitive L-lactate oxidase were not affected by 100 microM Cd2+, this indicates that the L-lactate oxidizing system lacks the accessible, cadmium-sensitive targets. The mechanism of Cd2+ toxicity to energy conservation with glutamate, pyruvate or L-lactate in S. aureus is discussed.
Tynecka
Z
Z
Department of Pharmaceutical Microbiology, Medical Academy, Lublin, Poland.
Malm
A
A
D000332:Aerobiosis; D002104:Cadmium / Q000633:toxicity*; D002462:Cell Membrane / Q000201:enzymology / Q000378:metabolism; D003470:Culture Media / Q000378:metabolism; D003593:Cytoplasm / Q000201:enzymology / Q000378:metabolism; D018698:Glutamic Acid / Q000378:metabolism; D019344:Lactic Acid / Q000378:metabolism; D006899:Mixed Function Oxygenases / Q000506:poisoning; D009097:Multienzyme Complexes / Q000506:poisoning; D009247:NADH, NADPH Oxidoreductases / Q000506:poisoning; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000506:poisoning*; D019289:Pyruvic Acid / Q000378:metabolism; D013211:Staphylococcus aureus / Q000201:enzymology* / Q000378:metabolism*
D003470:Culture Media; D009097:Multienzyme Complexes; D002104:Cadmium; D019344:Lactic Acid; D018698:Glutamic Acid; D019289:Pyruvic Acid; D006899:Mixed Function Oxygenases; D010088:Oxidoreductases; C021497:lactate 2-monooxygenase; C023107:NADH oxidase; D009247:NADH, NADPH Oxidoreductases