Q.Does our blood have proteases and nucleases?

Blood plasma does contain some enzymes, but the presence of proteases and nucleases is tightly regulated because uncontrolled activity of these enzymes would be catastrophic.

Proteases are present in blood, but they exist in inactive forms called zymogens or proenzymes. The blood clotting cascade is the clearest example—enzymes like prothrombin (inactive) are converted to thrombin (active protease) only when needed to form a clot. If active proteases circulated freely, they would digest blood proteins and damage tissues. The body also produces protease inhibitors that neutralize any stray active proteases. …

Our blood is a carefully regulated transport medium, and the presence—or rather, the deliberate absence—of certain enzymes tells us a great deal about how the body maintains internal stability. Proteases and nucleases are powerful digestive enzymes: proteases break down proteins into amino acids, while nucleases cleave nucleic acids (DNA and RNA) into nucleotides. If these enzymes were abundant in blood plasma, they would wreak havoc, digesting the very proteins and nucleic acids that cells need to function.

The digestive system is where proteases and nucleases do their main work. In the stomach and small intestine, enzymes like pepsin, trypsin, and chymotrypsin (proteases) and pancreatic DNase and RNase (nucleases) break down food molecules. These enzymes are secreted in inactive forms—zymogens—and activated only in the gut lumen, far from the delicate tissues of the body. This compartmentalization is crucial: digestion happens in a controlled space, not in the bloodstream.

Within cells, lysosomes house proteases and nucleases for intracellular digestion—breaking down worn-out organelles or engulfed pathogens. These enzymes are safely enclosed in membrane-bound vesicles, isolated from the cytoplasm. If a lysosome ruptures, the cell can be damaged, which underscores why such enzymes are never allowed to roam freely in extracellular fluids like blood. …

Method — ask "would free proteases/nucleases be safe here?" for each

• Proteases circulating actively would digest the blood's own structural/transport proteins → the body keeps them as inactive zymogens (e.g. prothrombin), activated only on demand (clotting). …