Prorenin () is a protein that constitutes a precursor for

renin Renin (etymology and pronunciation), also known as an angiotensinogenase, is an aspartic protease protein and enzyme secreted by the kidneys that participates in the body's renin–angiotensin–aldosterone system (RAAS)—also known as the r ...

, the hormone that activates the

renin–angiotensin system The renin–angiotensin system (RAS), or renin–angiotensin–aldosterone system (RAAS), is a hormone system that regulates blood pressure, fluid and electrolyte balance, and systemic vascular resistance. When renal blood flow is reduced, j ...

, which serves to raise

blood pressure Blood pressure (BP) is the pressure of circulating blood against the walls of blood vessels. Most of this pressure results from the heart pumping blood through the circulatory system. When used without qualification, the term "blood pressur ...

. Prorenin is converted into renin by the

juxtaglomerular cell Juxtaglomerular cells (JG cells), also known as juxtaglomerular granular cells are cells in the kidney that synthesize, store, and secrete the enzyme renin. They are specialized smooth muscle cells mainly in the walls of the afferent arter ...

s, which are specialised

smooth muscle Smooth muscle is an involuntary non- striated muscle, so-called because it has no sarcomeres and therefore no striations (''bands'' or ''stripes''). It is divided into two subgroups, single-unit and multiunit smooth muscle. Within single-unit ...

cells present mainly in the afferent, but also the efferent,

arteriole An arteriole is a small-diameter blood vessel in the microcirculation that extends and branches out from an artery and leads to capillaries. Arterioles have muscular walls (usually only one to two layers of smooth muscle cells) and are the pri ...

s of the glomerular capillary bed. Prorenin is a relatively large molecule, weighing approximately 46

KDa The dalton or unified atomic mass unit (symbols: Da or u) is a non-SI unit of mass widely used in physics and chemistry. It is defined as of the mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state and at re ...

History

Prorenin was discovered by Eugenie Lumbers in 1971.

Synthesis

In addition to juxtaglomerular cells, prorenin is also synthesised by other organs, such as the adrenal glands, the ovaries, the testis and the pituitary gland, which is why it is found in the plasma of anephric individuals.

Concentration

Blood concentration levels of prorenin are between 5 and 10 times higher than those of renin. There is evidence to suggest that, in

diabetes mellitus Diabetes, also known as diabetes mellitus, is a group of metabolic disorders characterized by a high blood sugar level (hyperglycemia) over a prolonged period of time. Symptoms often include frequent urination, increased thirst and increased ...

, prorenin levels are even higher. One study using relatively newer technology found that blood concentrations levels may be several order of magnitude higher than previously believed, and placing it at micrograms rather than nanograms per millilitre.

Pregnancy

Prorenin occurs in very high concentrations in

amniotic fluid The amniotic fluid is the protective liquid contained by the amniotic sac of a gravid amniote. This fluid serves as a cushion for the growing fetus, but also serves to facilitate the exchange of nutrients, water, and biochemical products betwe ...

and

amnion The amnion is a membrane that closely covers the human and various other embryos when first formed. It fills with amniotic fluid, which causes the amnion to expand and become the amniotic sac that provides a protective environment for the devel ...

. It is secreted in large amounts from the

placenta The placenta is a temporary embryonic and later fetal organ (anatomy), organ that begins embryonic development, developing from the blastocyst shortly after implantation (embryology), implantation. It plays critical roles in facilitating nutrien ...

and womb, and from the ovaries.

Conversion to renin

Proprotein convertase 1 Proprotein convertase 1, also known as prohormone convertase, prohormone convertase 3, or neuroendocrine convertase 1 and often abbreviated as PC1/3 is an enzyme that in humans is encoded by the ''PCSK1'' gene. PCSK1 and PCSK2 differentially cle ...

converts prorenin into renin, but proprotein convertase 2 does not. There is no evidence that prorenin can be converted into renin in the circulation. Therefore, the granular (JG) cells seem to be the only source of active renin.

References

{{Reflist

External links

RCSB PDB

PDBe
Proteins