Glycerol phosphorylation and oxidation in pancreatic islets

Area of Science:

• Biochemistry
• Cell Biology
• Metabolic Research

Background:

• Glycerokinase activity is essential for cellular metabolism.
• The role of glycerokinase in pancreatic islet cells, particularly concerning endogenous triglyceride metabolism, remains incompletely understood.

Purpose of the Study:

• To investigate the presence and characteristics of glycerokinase activity in rat pancreatic islets and RINm5F tumoral islet cells.
• To compare islet glycerokinase activity with that of the liver.
• To explore the relevance of glycerol metabolism in islet cell respiration.

Main Methods:

• Enzyme assays on homogenates of rat pancreatic islets and RINm5F cells.
• Subcellular fractionation to determine mitochondrial enzyme localization.
• Enzyme kinetics studies involving varying substrate (glycerol, ATP) concentrations and inhibitors (D-glyceraldehyde).
• Oxidation studies using [U-14C]glycerol in intact islets.

Main Results:

• Glycerokinase activity was detected in both rat pancreatic islets and RINm5F cells.
• Approximately one-sixth of the islet glycerokinase activity was found to be mitochondrially bound, similar to liver tissue.
• Enzymatic properties, including response to substrates and D-glyceraldehyde inhibition, differed between liver and islet glycerokinase.
• Intact islets efficiently oxidized [U-14C]glycerol, though at a lower rate than its phosphorylation in homogenates.

Conclusions:

• Rat pancreatic islets exhibit significant glycerokinase activity, with a portion localized to mitochondria.
• Islet glycerokinase displays distinct kinetic properties compared to liver glycerokinase.
• Glycerol derived from endogenous triglycerides likely contributes to the basal respiration of pancreatic islet cells.