Pools of Independently Cycling Inositol Phosphates Revealed by Pulse Labeling with ¹⁸O-Water

Area of Science:

• Cellular Biology
• Biochemistry
• Molecular Signaling

Background:

• Inositol phosphates are crucial for eukaryotic cellular processes like nutrient sensing, growth, and motility.
• Studying the dynamics of inositol phosphate signaling has been challenging due to limitations of traditional radioactive labeling methods, including slow uptake and stringent growth conditions.

Purpose of the Study:

• To develop a rapid, nonradioactive method for labeling and analyzing inositol polyphosphates and pyrophosphates in vivo.
• To investigate the phosphate group dynamics and metabolic organization of inositol phosphates in various cell types.

Main Methods:

• Utilized ¹⁸O-water labeling in yeast, human cells, and amoeba, applicable across different media.
• Combined ¹⁸O-water labeling with capillary electrophoresis and mass spectrometry for high-resolution analysis.
• Achieved temporal resolution from seconds to minutes to capture rapid molecular events.

Main Results:

• Demonstrated a novel, rapid (seconds to minutes) and nonradioactive labeling strategy for inositol phosphates using ¹⁸O-water.
• Successfully analyzed the in vivo phosphate group dynamics of a wide range of inositol phosphates, including rare ones.
• Observed significant differences in phosphate group exchange rates, with some inositol polyphosphates and pyrophosphates showing vigorous turnover while others remained inert.

Conclusions:

• Proposed a model of distinct, kinetically separated pools in the inositol polyphosphate and pyrophosphate biosynthetic pathway.
• These pools exhibit slow inter-pool transfer but rapid internal phosphate cycling, suggesting specialized signaling functions.
• This metabolic compartmentalization allows for diverse signaling roles while maintaining metabolic connectivity.