Phosphodiesterase 5A (PDE5A) is a key enzyme that regulates cellular signaling by hydrolyzing cyclic guanosine monophosphate (cGMP), a second messenger involved in smooth muscle relaxation and vasodilation. It is best known as the therapeutic target for sildenafil (Viagra) in treating erectile dysfunction and pulmonary arterial hypertension, where its inhibition increases cGMP levels to enhance blood flow. Research also explores its roles in cardiac function and cancer. Meanwhile, PDE5A can form a functional complex with ALDH7A1, an aldehyde dehydrogenase, potentially linking cGMP signaling to cellular metabolism and stress response pathways.Thus a functional ELISA assay was conducted to detect the interaction of recombinant PDE5A and recombinant ALDH7A1. Briefly, PDE5A was diluted serially in PBS with 0.01% BSA (pH 7.4). Duplicate samples of 100 μl were then transferred to ALDH7A1-coated microtiter wells and incubated for 1h at 37℃. Wells were washed with PBST and incubated for 1h with anti-PDE5A pAb, then aspirated and washed 3 times. After incubation with HRP labelled secondary antibody for 1h at 37℃, wells were aspirated and washed 5 times. With the addition of substrate solution, wells were incubated 15-25 minutes at 37℃. Finally, add 50 μL stop solution to the wells and read at 450/630nm immediately. The binding activity of recombinant PDE5A and recombinant ALDH7A1 was shown in Figure 1, the EC50?for this effect is 0.005μg/mL.