Question

What do you envision would happen metabolically if you selectively blocked the phosphate transporter (T3) within the ER lumen of hepatocytes?

Answer 1

The major role of the liver endoplasmic reticulum phosphate transport proteins is the regulation of blood glucose levels. The glucose-6-phosphatase enzyme is associated with transport proteins for the substrate glucose-6-phosphate (T1) and the products phosphate (T2) and glucose (T3). Glucose 6 phosphatase hydrolyzes glucose-6-phosphate to glucose and phosphate. Its active site is inside the lumen of the endoplasmic reticulum. The substrates and products of the enzyme, therefore, have to cross the endoplasmic reticulum membrane. Thus if T3 transporter is blocked the products formed by this enzyme glucose phosphatase will not be released from the lumen and there would be reduced release of glucose and phosphate. Hence blood glucose level will be reduced in the absence of phosphate transporter.