GPT and diabetes mellitus: The activity of several Glx consuming or producing enzymes (e.g. γ-glutamyltransferase [35-42], glutamine fructose-6-phosphate amidotransferase [43], glutamate pyruvate transaminase [40]) were reported to be associated with diabetes mellitus, impaired glucose tolerance and insulin resistance and are used as biomarkers to monitor liver functionality.