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Distribution of enzymes involved in mannan synthesis in plasma membranes and mesosomal vesicles of Micrococcus
Abstract:
The distribution of membrane-bound enzymes involved in mannan biosynthesis in plasma and mesosomal membranes of Micrococcus lysodeikticus has been investigated. Isolated mesosomal vesicles, unlike plasma membrane preparations, cannot catalyze the transfer of [14C]mannose from GDP-[14C]mannose into mannan. This appears to result from the inability of this membrane system to synthesize the carrier lipid [14C]mannosyl-1-phosphorylundecaprenol. In contrast, this is the major mannolipid synthesized from GDP-[14C]mannose by isolated plasma membranes. The possibility that substrate inaccessibility could account for the failure to detect the enzyme in isolated mesosomal vesicles appears unlikely from the lack of activity following disruption of the vesicles with ultrasound or with surface active agents. Both membrane preparations possessed the ability to catalyse the transfer of [14C]mannose from purified [14C]mannosyl-1-phosphorylundecaprenol into mannan. Furthermore, free mannan and mannan located on both unlabeled mesosomal and unlabeled plasma membranes could act as acceptors of [14C]mannosyl units from 14C-labeled carrier lipid located in prelabeled plasma membranes. The possibility that the juxtaposition of mesosomal vesicles and enveloping plasma membrane (i.e. the mesosomal sacculus) in vivo allows mannan, located on mesosomal vesicles, to accept mannosyl units from carrier lipid located in the sacculus membrane is discussed.
Insights
Micrococcus lysodeikticus plasma membranes synthesize mannan, unlike mesosomal vesicles. This difference in mannan biosynthesis is due to the mesosomal membranes' inability to produce the necessary carrier lipid.
Area of Science:
- Microbiology
- Cell Biology
- Biochemistry
Background:
- Mannan biosynthesis is crucial for bacterial cell wall structure.
- Understanding enzyme distribution in bacterial membranes provides insights into cellular processes.
Purpose of the Study:
- Investigate the localization and activity of mannan biosynthesis enzymes in Micrococcus lysodeikticus.
- Determine the specific membrane fractions responsible for mannan synthesis.
Main Methods:
- Isolation and characterization of plasma and mesosomal membrane vesicles.
- Enzymatic assays using GDP-[14C]mannose and [14C]mannosyl-1-phosphorylundecaprenol.
- Analysis of mannosyl-1-phosphorylundecaprenol synthesis.
Main Results:
- Plasma membranes efficiently synthesized [14C]mannosyl-1-phosphorylundecaprenol and mannan.
- Mesosomal vesicles failed to synthesize the carrier lipid and catalyze mannan formation from GDP-[14C]mannose.
- Both membrane types could transfer mannose from pre-synthesized [14C]mannosyl-1-phosphorylundecaprenol to mannan.
Conclusions:
- Plasma membranes are the primary site of mannan biosynthesis initiation in Micrococcus lysodeikticus.
- The absence of carrier lipid synthesis limits mannan biosynthesis in mesosomal membranes.
- In vivo proximity of membranes may facilitate mannan elongation in mesosomal vesicles.