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Membranes of the protoplast L-form of Proteus mirabilis
Abstract:
Isolated membranes of the cell wall-less stable protoplast L-form of Proteus mirabilis were characterized by density gradient centrifugation and by assay for their major chemical constituents, proteins, phospholipids and lipopolysacchartide, and for some specific marker enzymes of the cytoplasmic membrane. In most of the analyzed properties the L-form protoplast membrane resembled the bacterial cytoplasmic membrane, with some notable modifications. Considerable amounts of lipopolysaccharide, normally an exclusive constituent of the outer membrane, were found. Furthermore, the L-form membranes contained the functions of the reduced nicotinamide adenine dinucleotide oxidase system, of D-lactate dehydrogenase (EC 1.1.1.28) and of succinate dehydrogenase (EC 1.3.99.1) at specific activities comparable to, or in some cases considerably higher than, those present in cytoplasmic membranes of the bacterial form. Of two peptidoglycan DD-carboxypeptidase/transpeptidases (EC 3.4.17.8 and EC 2.3.2.10). which are normally present in the cytoplasmic membrane of the bacterial form of P. mirabilis, the membrane of the protoplast L-form contained only one. Electron microscopy of thin sectioned L-form protoplasts showed extensive heterogeneity of membraneous structures. In addition to the single membraneous integument, internal membrane-bounded vesicles and multiple stacks of membranes were present, as the result of unbalanced growth and membrane synthesis in the L-form state.
Insights
The cell wall-less Proteus mirabilis L-form protoplast membrane shares similarities with bacterial cytoplasmic membranes but contains significant lipopolysaccharide. This L-form membrane exhibits unique enzymatic activities and structural modifications due to unbalanced growth.
Area of Science:
- Microbiology
- Cell Biology
- Biochemistry
Background:
- The L-form of Proteus mirabilis is a stable, cell wall-less variant.
- Bacterial membranes, including cytoplasmic and outer membranes, have distinct compositions and functions.
- Understanding L-form membrane properties is crucial for studying bacterial adaptation and cell envelope biology.
Purpose of the Study:
- To characterize the isolated membranes of the Proteus mirabilis L-form protoplast.
- To compare the biochemical and enzymatic properties of L-form membranes with those of the parental bacterial form.
- To investigate the structural organization of L-form membranes using electron microscopy.
Main Methods:
- Density gradient centrifugation was used to isolate and purify L-form membranes.
- Assays were performed to quantify major chemical constituents: proteins, phospholipids, and lipopolysaccharide.
- Specific marker enzymes of the cytoplasmic membrane, including oxidases and dehydrogenases, were analyzed.
- Electron microscopy was employed to examine the ultrastructure of L-form protoplasts.
Main Results:
- L-form protoplast membranes showed similarities to bacterial cytoplasmic membranes but contained considerable amounts of lipopolysaccharide, typically found in the outer membrane.
- Enzymatic activities of reduced nicotinamide adenine dinucleotide oxidase, D-lactate dehydrogenase, and succinate dehydrogenase were comparable or higher in L-form membranes than in bacterial cytoplasmic membranes.
- Only one of the two peptidoglycan DD-carboxypeptidase/transpeptidases found in the bacterial form was present in the L-form membrane.
- Electron microscopy revealed heterogeneous membranous structures within L-form protoplasts, including internal vesicles and stacked membranes, indicative of unbalanced growth.
Conclusions:
- The Proteus mirabilis L-form protoplast membrane exhibits a unique composition, blending characteristics of both cytoplasmic and outer bacterial membranes.
- The observed enzymatic activities and structural heterogeneity suggest significant alterations in membrane synthesis and organization in the L-form state.
- These findings provide insights into the adaptive membrane biology of bacterial L-forms.