Catalyzes the interconversion of glyceraldehyde 3-phosphate and dihydroxyacetone phosphate in the glycolytic and gluconeogenic pathways. D-glyceraldehyde 3-phosphate = dihydroxyacetone phosphate kcat is 4300 sec(-1) with D-glyceraldehyde-3-phosphate as substrate (at 25 degrees Celsius) (PubMed:26762569). kcat is 4233 sec(-1) with D-glyceraldehyde-3-phosphate as substrate (at pH 7.6) (PubMed:19622869). Carbohydrate biosynthesis; gluconeogenesis. Carbohydrate degradation; glycolysis; D-glyceraldehyde 3-phosphate from glycerone phosphate: step 1/1. Homodimer. Belongs to the triosephosphate isomerase family.