Based on that data, they found that a protein responsible for transporting glucose -; a kind of sugar -; into cells was present in significantly higher levels in lung SqCC than in lung ADC. The protein, called glucose transporter 1, or GLUT1, takes up glucose into cells, where the sugar provides a fundamental energy source and fuels cell metabolism. GLUT1 is also necessary for normal cell function, such as building cell membranes.