Enables glutamate dehydrogenase (NAD+) activity. Involved in glutamine metabolic process and tricarboxylic acid metabolic process. Acts upstream of or within positive regulation of insulin secretion. Located in mitochondrial matrix. Is expressed in several structures, including alimentary system; central nervous system; metanephros; respiratory system; and sensory organ. Human ortholog(s) of this gene implicated in familial hyperinsulinemic hypoglycemia 6; hyperinsulinism; hypoglycemia; and late onset Parkinson's disease. Orthologous to several human genes including GLUD1 (glutamate dehydrogenase 1). [provided by Alliance of Genome Resources, Apr 2022]