Functional studies of yeast glucokinase

Area of Science:

• Biochemistry and Molecular Biology
• Yeast Metabolism and Genetics

Background:

• Glucose phosphorylation capacity typically exceeds glucose flux in wild-type Saccharomyces cerevisiae.
• A mutant strain lacking hexokinases but retaining glucokinase presents a unique model for studying glucose metabolism.

Purpose of the Study:

• To investigate the role of glucokinase in glucose transport and phosphorylation in Saccharomyces cerevisiae.
• To determine if increased glucokinase activity can enhance glucose flux in the absence of hexokinases.

Main Methods:

• Comparative analysis of glucose flux and internal glucose concentration in wild-type and glucokinase-dependent mutant strains.
• Measurement of radioactive glucose uptake under various conditions, including glucose and maltose batch cultures.
• Enzymatic activity assays of glucokinase and hexokinase following toluene treatment.

Main Results:

• Internal glucose concentration remains low during active growth on glucose in both wild-type and mutant strains.
• Additional glucokinase activity does not elevate glucose flux.
• The glucokinase-dependent strain accumulates significant internal glucose after external glucose depletion or when grown on maltose.
• Radioactive glucose uptake shows incomplete mixing with the internal pool in these accumulation scenarios.
• Glucokinase activity is minimally detected after toluene treatment, unlike hexokinase.

Conclusions:

• The findings suggest a potential link between glucose entry into the cell and its subsequent phosphorylation by glucokinase.
• Separate mechanisms may explain the observed glucose accumulation and incomplete mixing phenomena.
• Glucokinase's role in yeast glucose metabolism, particularly in relation to transport, warrants further investigation.