The term 'kidney enzyme' refers to renin, a five-letter protein produced by the kidneys. Renin is an enzyme that plays a role in regulating blood pressure and electrolyte balance. It is released into the bloodstream when the kidneys detect a decrease in blood pressure or sodium levels. Renin then acts on a hormone called angiotensinogen, converting it into angiotensin I, which is then converted into angiotensin II. Angiotensin II causes blood vessels to constrict, increasing blood pressure and helping to restore normal levels.