Table 2.

Glucose transporter proteins.²⁶,²⁷

ISOFORM	Tissue Distribution	Affinity for Glucose	Km	Characteristics	Gene location
GLUT 1	Brain microvessels,			Ubiquitous
	Red blood cells	High	1 mmol/L		Chr 1
	Placenta			Basal transporter
	Kidney
	All tissues
GLUT 2	Liver			High Km transporter
	Kidney	Low	15–20 mmol/L		Chr 3
	β cell			Insulin-independent
	Small intestine
GLUT 3	Brain neurons			Low Km transporter
	Placenta	High	<1 mmol/L		Chr 12
	Foetal muscle			Found in glucose- dependent tissues
	All tissues
GLUT 4	Muscle cells			Sequestered intracellularly and translocates to cell surface in response to insulin
	Fat cells	Medium	2.5–5 mmol/L		Chr 17
	Heart
GLUT 5	Small intestine			High affinity for fructose
	Testes	Medium	6 mmol/L		Chr 1