Amino acids combine to form peptides and proteins

In nature, the amino acids are combined to give proteins with hundreds or even thousands of amino acids in each one. Small assemblies of amino acids are known as peptides and the amide bond that links them is called a peptide bond. An important tripeptide is glutathione, present in the tissues of both animals and plants. Glutathione is the ‘universal thiol’ that removes dangerous oxidizing agents by allowing itself to be oxidized to a disulfide. Glutathione is, however, not quite a typical tripeptide. The left-hand amino acid is normal glutamic acid but it is joined to the next amino acid through its γ-CO₂H group instead of the more normal α-CO₂H group. The middle amino acid is the vital one for the function—cysteine with a free SH group. The C-terminal acid is glycine.

Thiols are easily oxidized to disulfides and glutathione sacrifices itself if it meets an oxidizing agent. The oxidized form of glutathione can later be converted back to the thiol by reduction with NADH.

With a stray oxidizing agent such as a peroxide, say H₂O₂, the mechanism below shows how this can be reduced to water as glutathione (represented as RSH) is oxidized to a disulfide.

Glutathione also detoxifies some of the compounds we described earlier in this book as dangerous carcinogens such as Michael acceptors and 2,4-dinitrohalobenzenes. The thiol acts as a nucleophile, inactivating the electrophiles. Covalently bound to glutathione they are harmless and can be excreted. More glutathione will be synthesized from glutamic acid, cysteine, and glycine to replace that which is lost.

Some short peptides, of around ten amino acids, are hormones. Angiotensin II, for example, is a peptide that causes blood pressure to rise—a very necessary thing in some situations but too much and too often leads to heart attacks and strokes. Angiotensin-converting enzyme (ACE) is the zinc-dependent enzyme that cleaves two amino acids from the end of angiotensin I to give angiotensin II, and ACE inhibitors are used as treat ment for high blood pressure because they inhibit this enzyme. Lisinopril is an example: it is a dipeptide mimic, having two natural amino acids and something else. The ‘something else’ is the left-hand part of the molecule, linked to the dipeptide (Lys–Pro) through an amine and not by an amide bond. This stops enzymes from hydrolysing the molecule. Lisinopril binds to ACE because it is like a natural dipeptide but it inhibits it because it is not a natural dipeptide. Many people are alive today because of this simple deception practised on an enzyme.

اخر الاخبار

اخبار العتبة العباسية المقدسة

معمل مياه الكفيل: عمل على مدار الساعة دون توقف لتلبية الطلب المتزايد على المياه

مركز الكفيل للصحة والسلامة: برنامج الإخلاء الطبي غطى جميع الجوانب المتعلقة بالإسعاف الطارئ

أنشطة قرآنية وعزائية للمجمع العلمي في النجف الأشرف وبغداد

أستاذ الحوزة العلمية الشيخ حسن الجواهري يطلع على الخدمات الثقافية للزائرين في مجمع أبي الفضل العباس (عليه السلام)

المزيد

الآخبار الصحية

حجم جزء محدد من الجسم يعكس الصحة العامة ومخاطر الأمراض

تفشي عدوى بكتيرية بفرنسا يحتمل ارتباطها بنوع من الجبن الطري

دراسة حديثة تكشف ما تفعله الشاشات بـ"قلوب الأطفال" !

متلازمة المبنى المريض.. هكذا يتحول تكييف الهواء إلى خطر صحي ؟؟

المزيد

الآخبار التكنلوجية

كيف تتعامل مع حرارة الطقس أثناء القيادة؟

لماذا يجب عليك إيقاف تكييف السيارة قبل إطفاء المحرك؟

دراسة تكشف سببا محتملا وراء زيادة خطر إصابة الأطفال بالتوحد

تشيلي.. العثور على متحجرة حيوان ثديي صغير من زمن الديناصورات

المزيد

مواضيع ذات صلة

Lipids

Most sugars are embedded in complex carbohydrates

Glycosides in nature

Sugars can be fixed in one shape by acetal formation

Sugars normally exist in cyclic forms with much stereochemistry

Antiobiotics exploit the special chemistry of bacteria

Proteins are made of amino acids

Cyclic nucleosides and stereochemistry

HIV and AIDS are treated with modifi ed nucleosides Modified nucleosides

The stimulants in tea and coffee are methylated purines

Life begins with nucleic acids

Aldol reactions catalysed by proline