In vitro formation of glucose-6-phosphate from glyceraldehyde-3-phosphate by liver cytosol from fed and starved rats. Effect of divalent cations on the conversion rate.

Liver cytosol preparations from fed rats are shown to form glucose-6-phosphate from glyceraldehyde-3-phosphate at a rate of 1.6 μmoles·min^?1·g liver wet weight^?1 in presence of 0.4 mM Mg²⁺. This rate is more than doubled by 30 μM EGTA and/or Mg²⁺-concentrations ≥2 mM. 48 hours starvation increases the rate of glucose-6-phosphate formation at 0.4 mM Mg²⁺ to 3.0 μmoles·min^?1·g liver wet weight^?1 and greatly diminishes the effect of EGTA and of higher Mg²⁺-concentrations. Inhibition of glucose-6-phosphate formation by Ca²⁺ and Zn²⁺ is shown to be more pronounced with cytosol from fed than from 48 hours starved rats.