19. Consider the picture: This reaction is catalyzed by an enzyme glyceraldehyde.phosphate dehydrogenase triose phosphate isomerase fructose-1,6-diphosphate aldolase phosphoglycerate kinase

The question is asking about the enzyme that catalyzes the reaction shown in the picture. The reaction is the conversion of glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate. This reaction is catalyzed by the enzyme glyceraldehyde 3-phosphate dehydrogenase. Therefore, the correct answer is "glyceraldehyde 3-phosphate dehydrogenase".