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Cation-binding capacity of membranes isolated from Micrococcus lysodeikticus
Abstract:
A study was made of H(+), Na(+), K(+), Ca(++), and Mg(++) binding and ion-exchange properties of the plasma-mesosome membrane system isolated from Micrococcus lysodeikticus strain NCTC 2665. Titration curves were obtained on membranes prepared according to the method of M. R. J. Salton and further exposed to pH 4 for 4 hr (membranes-H). The dissociation coefficients and binding capacities were obtained by applying the mass law equation and the plot of G. Schatchard to the data. The membranes-H possess four kinds of dissociable groups with pK 4.96, 4.18, 3.60, and 3.09, respectively, and a total binding capacity of 0.65 meq/g (dry weight). Potentiometric titrations of cations in the presence and in the absence of membranes-H show that cations (Na(+), K(+), Ca(++), and Mg(++)) are bound by the dissociated groups of the membrane. The fall in pH value for bivalent cations is greater than that for monovalent cations. Cations of the same valency produce equal diminutions on pH. Furthermore, ion-exchange tests carried out on membranes saturated with Mg(++) or Na(+) and suspended in a medium containing (45)Ca show that the cations are reversibly bound.
Insights
Micrococcus lysodeikticus membranes bind various cations, including H(+), Na(+), K(+), Ca(++), and Mg(++), through dissociable groups. These cations are reversibly bound, demonstrating ion-exchange properties crucial for membrane function.
Area of Science:
- Microbiology
- Biochemistry
- Membrane Biophysics
Background:
- The plasma-mesosome membrane system of Micrococcus lysodeikticus is crucial for cellular processes.
- Understanding ion binding and exchange properties is vital for elucidating membrane function.
Purpose of the Study:
- To investigate the cation binding and ion-exchange characteristics of Micrococcus lysodeikticus membranes.
- To determine the dissociation coefficients and binding capacities of membrane components for various cations.
Main Methods:
- Isolation of the plasma-mesosome membrane system from Micrococcus lysodeikticus.
- Preparation of membranes-H by exposure to pH 4.
- Potentiometric titrations and ion-exchange tests using radiolabeled calcium (45Ca).
- Application of the mass law equation and Scatchard plot analysis.
Main Results:
- Membranes-H exhibit four types of dissociable groups with pK values of 4.96, 4.18, 3.60, and 3.09.
- Total binding capacity of the membranes is 0.65 meq/g (dry weight).
- Cations (Na(+), K(+), Ca(++), Mg(++)) are bound by dissociated membrane groups, with bivalent cations causing a greater pH decrease than monovalent cations.
- Ion-exchange tests confirm reversible cation binding.
Conclusions:
- The plasma-mesosome membrane system of Micrococcus lysodeikticus possesses significant cation binding and ion-exchange capabilities.
- The identified dissociable groups and binding capacities provide insights into the membrane's interaction with cations.
- These properties are essential for maintaining cellular ion homeostasis and function.