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Effect of spermine on the uptake of amino acids in Micrococcus lysodeikticus
Abstract:
Spermine inhibited the transport of neutral aliphatic amino acids (valine, leucine, isoleucine, alanine, and glycine) into cells of Micrococcus lysodeikticus. On the other hand, spermine did not affect the uptake of basic (arginine and histidine), acidic (glutamic acid), or aromatic (phenylalanine and tyrosine) amino acids. Inhibition of uptake of the neutral amino acids by spermine is apparently of a noncompetitive nature; the V(max) decreased, whereas the apparent K(m) remained unaltered. The inhibition is most likely due to a specific binding of spermine to the carrier(s) of these amino acids. Related polyamines, spermidine and cadaverine, also caused inhibition of valine uptake, though to a lesser extent; spermidine was less active than spermine, and cadaverine showed the weakest effect of all. Valine, leucine, and isoleucine were transported into M. lysodeikticus cells by a common carrier as evidenced from competition experiments. The uptake of these amino acids is an active process; it was temperature-dependent and inhibited by azide (10(-1)m to 2.5 x 10(-2)m) and dinitrophenol (10(-3)m). The intracellular concentration of valine was 100-fold higher than in the medium.
Insights
Spermine specifically inhibits the transport of neutral amino acids into Micrococcus lysodeikticus cells. This noncompetitive inhibition suggests spermine binds to the amino acid carriers, impacting bacterial nutrient uptake.
Area of Science:
- Microbiology
- Molecular Biology
- Biochemistry
Background:
- Amino acid transport is crucial for bacterial cell function and survival.
- Polyamines play diverse roles in cellular processes, including nucleic acid and protein synthesis.
- Micrococcus lysodeikticus is a Gram-positive bacterium used in microbiological studies.
Purpose of the Study:
- To investigate the effect of spermine on amino acid uptake in Micrococcus lysodeikticus.
- To determine the specificity and mechanism of spermine-mediated inhibition of amino acid transport.
- To identify the nature of the amino acid transport systems affected by polyamines.
Main Methods:
- Utilized uptake assays to measure the transport of various radiolabeled amino acids into bacterial cells.
- Performed kinetic analyses (Vmax, Km) to characterize the inhibition mechanism.
- Conducted competition experiments to identify common transport carriers.
- Investigated the effect of related polyamines (spermidine, cadaverine) on amino acid uptake.
Main Results:
- Spermine significantly inhibited the uptake of neutral aliphatic amino acids (valine, leucine, isoleucine, alanine, glycine) but not basic, acidic, or aromatic amino acids.
- The inhibition by spermine was noncompetitive, decreasing Vmax while leaving Km unchanged, indicating specific carrier binding.
- Spermidine and cadaverine also inhibited valine uptake, but to a lesser extent than spermine.
- Competition experiments revealed a common carrier for valine, leucine, and isoleucine.
- Amino acid uptake was confirmed as an active, temperature-dependent process sensitive to metabolic inhibitors like azide and dinitrophenol.
Conclusions:
- Spermine selectively inhibits the transport of neutral aliphatic amino acids in Micrococcus lysodeikticus via specific binding to their carriers.
- The transport of valine, leucine, and isoleucine is mediated by a shared active transport system.
- Polyamines can modulate bacterial amino acid transport, suggesting a role in nutrient regulation.