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Changing pattern of cyclic AMP-binding proteins during germination of Mucor racemosus sporangiospores
Abstract:
Interation of cyclic AMP with a profoundly changing pattern of specific binding proteins was shown during aerobic germination of sporangiospores from the fungus Mucor racemosus. 32P-labeled 8-azido-cycli AMP, an analogue of cyclic AMP that forms a covalent linkage with the binding proteins under u.v. light, was used as the ligand. Binding proteins carrying this photoaffinity label were separated by polyacrylamide-gel electrophoresis and identified by radioautography. Equibiltrium dissociation constants (Kd) and binding-response curves in the presence of competing nucleotides were identical for both 8-azido-cyclic [32P]AMP and cyclic [3H]AMP. A quantitative binding assay with both 8-azido-cyclic [32P]AMP and cyclic [3H]AMP over the time course of sporangiospore germination indicated a parallel relationship between cyclic AMP-binding capacity and the intracellular concentrations of cyclic AMP reported in a previous study [Paznokas & Sypherd (1975) J. Bacteriol. 124, 134--139]. Both of these parameters attained transient high values at a time of development when addition of exogenous cyclic AMP prevents hyphal-germ-tube emergence. The measured Kd values did not change during sport germination.
Insights
During fungal spore germination, cyclic AMP (cAMP) interacts with specific binding proteins. These interactions change significantly, influencing hyphal development and spore germination.
Area of Science:
- Mycology
- Molecular Biology
- Biochemistry
Background:
- Cyclic AMP (cAMP) is a crucial second messenger in various cellular processes.
- Fungal spore germination involves complex regulatory mechanisms.
- Specific cAMP-binding proteins are implicated in fungal development.
Purpose of the Study:
- To investigate the interaction of cyclic AMP with specific binding proteins during fungal spore germination.
- To characterize the changes in cAMP-binding capacity throughout germination.
- To correlate cAMP-binding protein activity with developmental transitions.
Main Methods:
- Utilized 32P-labeled 8-azido-cyclic AMP, a photoaffinity analog of cAMP, for covalent labeling.
- Separated and identified labeled binding proteins using polyacrylamide-gel electrophoresis and radioautography.
- Performed quantitative binding assays with both 8-azido-cyclic [32P]AMP and cyclic [3H]AMP.
Main Results:
- Demonstrated a dynamic pattern of specific cAMP-binding proteins during aerobic germination of Mucor racemosus sporangiospores.
- Confirmed that 8-azido-cyclic AMP accurately labels cAMP-binding proteins, with identical binding affinities (Kd) compared to cyclic [3H]AMP.
- Observed a parallel relationship between cAMP-binding capacity and intracellular cAMP concentrations.
- Noted that both parameters peaked transiently during a developmental stage where exogenous cAMP inhibits germ-tube emergence.
Conclusions:
- Specific cAMP-binding proteins undergo significant changes during fungal spore germination.
- The observed changes in cAMP-binding capacity are directly linked to intracellular cAMP levels.
- These cAMP-binding proteins play a critical role in regulating the transition from spore to hyphal growth.