The Nobel Prize in Physiology and Medicine was awarded in 1999 for the discovery in the early 1980s that the gas nitric oxide was found to be a hormone in the cardiovascular system. The recipients of the award were R.F. Furchgott, L.J. Ignarro, and F. Murad.

Biochemical properties of the nitric acid synthase enzyme. Nitric acid (NO) is enzymatically produced from the amino acid L-arginine by a Ca2+ dependent NO synthase that is present in many mammalian tis sues. Particularly arteries and their endothelial cells are able to produce NO.

The formation and production of NO is an enzyme mediated reaction; see Figures 1A and 1B. Nitric oxide synthases (NOS) are a family of three enzymes catalyzing the production of nitric oxide (NO) from L-arginine. Each of the three NOS enzymes is encoded by different genes. The nitrogen donor is the amino acid L-arginine and the oxygen donor is molecular oxygen. The reaction is catalyzed by an NADPH requiring the nitric oxide synthase (NOS). NOS enzymes are structurally related to cytochrome P450 reductase  and range in size from 130 to 160 kDa. NOS exists as a constitutive enzyme, which is regulated by both the intracellular Ca2+ and the calcium-binding protein, calmodulin.

Fig1. The gas, nitric oxide, is a hormone that initiates vasorelaxation and lowers blood pressure. (A) Biochemical properties of the nitric acid synthase enzyme. Nitric acid (NO) is enzymatically produced from the amino acid L-arginine by a Ca2+ dependent NO synthase that is present in many mammalian tissues. The reaction is catalyzed by an NADPH requiring nitric oxide synthase (NOS). The nitrogen donor (colored red) is located on the guanidino group of the side chain of the amino acid substrate L-arginine. The oxygen donor (colored red) is molecular oxygen. The final products of the enzymatic reaction are the release of the gas nitric oxide, NO, and the amino acid L-citrulline. (B) Nitric oxide signalling pathways that generate biological responses in both endothelial cells and smooth muscle cells. Endothelial cells have a variety of supporting signal transduction pathways that lead to the activation of nitrogen oxide synthase, which then diffuses to adjacent smooth muscle cells. Here it enters the cell and, via signal activation, causes the smooth muscle cell to engage in lowering the blood pressure because of reduction of peripheral vascular resistance and at the same time increase. Ultimately the generation of NO leads to relaxation of both the endothelial cells and its partner smooth muscle cell(s). In these cells there is guanylyl cyclase that has a heme group that binds the NO hormone, thus activating the production of the second messenger, cGMP, which results in muscle relaxation.

The hormone NO is a free radical gas that has a limited solubility in water. As previously mentioned, a very helpful property is that, because NO is not charged, it is readily able to diffuse from endothelial cells through the cellular membrane and gain entry into nearby cells, such as smooth muscle cells where biological responses can be initiated. However, NO is inherently unstable. The time interval from its enzymatic formulation to its chemical breakdown is only several seconds. The NO undergoes spontaneous chemical oxidation to either nitrate (NO3⁻) or nitrite (NO2⁻ ), neither of which has hormonal or biological activities. However, since there is an excess of the NO synthase enzyme, there is no difficulty in maintaining a continuous availability of NO in the local environment. NO binds to its receptor in the low nanomolar (10⁻⁹ M) concentration range.

اخر الاخبار

اخبار العتبة العباسية المقدسة

قسم الصيانة يقيم دورة تدريبية عن آلية تنصيب مطافئ الحريق اليدوية وإدامتها لملاكاته

قسم الشؤون الخدمية ينفذ حملة لغسل محيط العتبة العباسية المقدسة وتنظيفه

ضمن برنامج تأهيل المنتسبين الجدد.. قسمُ الشؤون الدينية يطلق دورته الفقهية الـ59 لمنتسبي العتبة العباسية المقدسة

ضمن مقتنياته التراثية.. متحف الكفيل يوثّق تاجًا ذهبيًّا مرصَّعًا بالأحجار الكريمة

المزيد

الآخبار الصحية

المركز الاوروبي : كل ركاب سفينة "هانتا" مخالطون معرضون لخطر كبير

ألمانيا.. رئيس الأطباء يدعو للإسراع بتطبيق "ضريبة السكر"

بين الفائدة والضرر.. جدل حول تأثير الشاي والقهوة على العظام

أمراض خطيرة.. أبحاث تكشف مخاطر الجلوس لفترة طويلة

المزيد

الآخبار التكنلوجية

سبع حقائق غير متوقعة عن موجات الراديو

الأجسام الغريبة.. ماذا رأى رواد "أبولو 17" على القمر؟

حرارة المحيطات عند مستويات مقلقة.. وعودة "إل نينيو" تقترب

باحثون يحددون تأثير القهوة على الميكروبيوم والمزاج

المزيد

مواضيع ذات صلة

Chemistry, Biosynthesis, and Secretion of Endothelins

Chemistry, Biosynthesis, and Secretion of ANP

Hemoglobins with Increased Oxygen Affinity

Specific Enzymes are Associated with Compartments Separated by the Mitochondrial Membranes

ATP Acts as the “Energy Currency” of The Cell

Living Organisms Package Transition Metals Within Organometallic Complexes

Androgen Biosynthesis

Androgens and Related Molecules

Two-Dimensional Polyacrylamide Gel Electrophoresis

Isoelectric Focussing Gels

Native (Buffer) Gels

Sodium Dodecyl Sulfate (SDS)-Polyacrylamide Gel Electrophoresis