An enquiry into metabolite domains

Area of Science:

• Biochemistry
• Cell Biology
• Physical Chemistry

Background:

• Mammalian cells are theorized to contain distinct cytosolic metabolite pools.
• These pools are hypothesized to arise from the spatial organization of enzymes and transporters.
• This concept is analogous to calcium microdomain formation.

Purpose of the Study:

• To develop an analytical tool to estimate the spatial dimensions and concentration gradients of metabolite pools.
• To investigate the physical chemistry basis of metabolite distribution within the cell cytosol.
• To reevaluate the concept of cytosolic metabolite compartmentation.

Main Methods:

• Development of an analytical tool based on Brownian diffusion.
• Incorporation of protein turnover rates into the diffusion model.
• Application of the tool to various metabolites including ATP, glucose, pyruvate, lactate, and glutamate.

Main Results:

• Common metabolites like ATP, glucose, pyruvate, lactate, and glutamate do not form significant concentration gradients at their sources.
• The cytosol behaves as a homogenous compartment for metabolites present at micromolar concentrations or higher.
• Calcium and pH nanodomains were identified near slow enzymes and transporters, but not for the studied metabolites.

Conclusions:

• The prevailing notion of distinct cytosolic metabolite pools requires reevaluation.
• The physical chemistry of diffusion and enzyme kinetics suggests a well-mixed cytosol for many metabolites.
• Further investigation into metabolite compartmentation is warranted, considering physical and chemical principles.