Glucose transport in Achlya: characterization and possible regulatory aspects

Area of Science:

• Mycology
• Cell Biology
• Biochemistry

Background:

• The freshwater fungus *Achlya* exhibits nutrient transport mechanisms crucial for its survival.
• Understanding sugar uptake in fungi is vital for comprehending their metabolic processes and ecological roles.

Purpose of the Study:

• To elucidate the mechanism of D-(+)glucose and 2-deoxy-D-glucose transport in *Achlya*.
• To identify factors influencing and potentially regulating glucose uptake in this freshwater fungus.

Main Methods:

• Investigated glucose and deoxyglucose transport kinetics in *Achlya* under various conditions.
• Utilized metabolic inhibitors, competing sugars, pH, and temperature variations to probe transport specificity and energy dependence.
• Employed osmotic shock treatments to isolate and characterize cell wall/membrane components involved in transport.
• Analyzed intracellular products of glucose transport, specifically phosphorylation.

Main Results:

• Glucose and deoxyglucose transport are energy-dependent, inhibited by metabolic uncouplers and specific competing sugars, indicating a degree of specificity.
• Transport is optimal at pH 6.5 and 30-40°C.
• Inhibition of transport by external agents (citrate, N6-substituted adenines, iodine) without cell penetration suggests membrane-associated interactions.
• Osmotic shock disrupted glucose transport by releasing a phosphorylated proteoglycan (PPG), which was essential for transport until resynthesized.
• Intracellular glucose was rapidly phosphorylated to glucose-6-phosphate, suggesting phosphorylation occurs during transport.

Conclusions:

• *Achlya* utilizes a specific, energy-dependent transport system for glucose uptake.
• A cell wall/membrane-associated phosphorylated proteoglycan (PPG) plays a critical role in glucose transport.
• External compounds interacting with PPG, calcium, or HS compounds may modulate glucose transport by altering membrane structure or function.