Neutral-sugar transport by rat liver lysosomes

Area of Science:

• Cell Biology
• Biochemistry
• Molecular Transport

Background:

• Lysosomes are key organelles involved in cellular degradation.
• Understanding lysosomal transport is crucial for cellular homeostasis and metabolic processes.
• Specific mechanisms for lysosomal sugar uptake remain incompletely characterized.

Purpose of the Study:

• To investigate the transport system for D-glucose in rat liver lysosomes.
• To identify the characteristics and specificity of lysosomal D-glucose uptake.
• To differentiate lysosomal sugar transport from other cellular sugar transport mechanisms.

Main Methods:

• Utilized Percoll-gradient-purified rat liver lysosomes.
• Assessed D-glucose uptake kinetics (Km, t1/2).
• Performed competitive inhibition studies with various sugars and amino acids.
• Investigated effects of chemical agents, ATP, and pH on uptake.
• Studied D-glucose and L-fucose efflux and their inhibition.

Main Results:

• D-glucose uptake exhibited a Km of 22 mM and a half-life of approximately 30 seconds.
• D-fucose, 2-deoxyglucose, and methyl alpha-glucoside were potent inhibitors of D-glucose uptake.
• Uptake was unaffected by various chemical agents, ATP/Mg, or buffer pH changes.
• D-glucose efflux was temperature-dependent (Q10=2.3) and inhibited by cytochalasin B.
• L-fucose uptake (Km=65 mM) was distinct and also inhibited by cytochalasin B.

Conclusions:

• Rat liver lysosomes possess a facilitated transport system for D-glucose.
• This system appears specific for neutral D-sugars and distinct from transport systems for acetylated or acidic sugars.
• Lysosomal sugar transport mechanisms are specialized and regulated, with cytochalasin B affecting both D-glucose and L-fucose transport.