The correct answer for the enzyme that is secreted by the kidney and responsible for converting plasma protein angiotensinogen into angiotensin is option 1: Renin.

Renin is an enzyme that is produced and secreted by specialized cells in the kidneys called granular cells or juxtaglomerular cells. It plays a crucial role in the renin-angiotensin-aldosterone system, which helps regulate blood pressure and fluid balance.

When the blood pressure in the kidneys drops or there is a decrease in blood flow to the kidneys, it stimulates the release of renin. Renin then acts on angiotensinogen, a protein produced by the liver and released into the bloodstream. Renin cleaves angiotensinogen to produce angiotensin I. Angiotensin I is further converted to angiotensin II by an enzyme called angiotensin-converting enzyme (ACE), which is primarily found in the lungs. Angiotensin II is a potent vasoconstrictor, meaning it narrows the blood vessels, causing an increase in blood pressure.

Therefore, the correct enzyme secreted by the kidney, which changes plasma protein angiotensinogen into angiotensin, is