Nature’s NaBH4 is a nucleotide: NADH or NADPH

You met nucleotides, and their role in the structure of nucleic acids, earlier in this chapter. Nature also uses nucleotides as reagents. Here is the structure of AMP, just to remind you of a structure you met before, side by side with a pyridine-containing nucleotide.

These two nucleotides can combine together as a pyrophosphate to give a dinucleotide called nicotinamide adenine dinucleotide, or NAD (or NAD+—note the positively charged pyridinium). Notice that the link is not at all the same as in the nucleic acids. The latter are joined by one phosphate that links the 3′ and 5′ positions. Here we have a pyrophosphate link between the two 5′ positions.

The positively charged pyridinium ring is the part of the molecule which does all the work and from now on we will draw only the reactive part for clarity. NAD+ is one of nature’s most important oxidizing agents. Some biochemical pathway reactions use NADP instead, but this differs only in having an extra phosphate group on the adenosine portion so the same part structure will do for both. NAD+ and NADP both work by accepting a hydrogen atom and a pair of electrons from another compound. The reduced compounds are called NADH and NADPH.

The reduction of NAD+ (and NADP) is reversible, and NADH is itself a reducing agent. We will first look at one of its reactions: a typical reduction of a ketone. The ketone is pyruvic acid and the reduction product is lactic acid—both important metabolites. The reaction is cata lysed by an alcohol dehydrogenase.

This is a reaction that would also work in the laboratory with NaBH4 as the reducing agent, but there is a big difference. The product from the NaBH4 reaction must be racemic—the start ing material, reagent, and solvent are all achiral.

But the product from the enzymatic reaction is optically active. The two faces of pyruvic acid’s carbonyl group are enantiotopic and, by controlling the addition so that it occurs from one face only, the enzyme-catalysed reaction gives a single enantiomer of lactic acid.

اخر الاخبار

اخبار العتبة العباسية المقدسة

خدمات فكرية وثقافية عديدة قدمها مركز مُلتقى القمر الثقافي لزائري الأربعين

إحياءً لذكرى زيارة الأربعين.. العتبة العباسية المقدسة تواصل إقامة مجلسها العزائي

عبر كاميرات تعمل بالذكاء الاصطناعي.. قسم الاتصالات يوضح تفاصيل جديدة حول آلية عدِّ زائري الأربعين

شعبة الخطابة الحسينية النسوية تواصل نشاطاتها الفكرية والثقافية في مجمع الشيخ الكليني

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

Pyrrolidine alkaloids are made from the amino acid ornithine

Alkaloids are made by amino acid metabolism

The shikimic acid pathway

Phosphoenolpyruvate

Nature’s enolate equivalents: lysine enamines and coenzyme A

Reductive amination in nature

Oil and water do not mix

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