The primary enzyme that catalyzes the cleavage of the side chain of cholesterol to initiate the process of steroidogenesis is P450scc that produces as its product pregnenolone (see Figure 1). The p450scc is known as a lyase. Lyases are enzymes that cleave bonds between carbons bearing vicinal hydroxyls. The proper ties of these two reactions will be discussed separately.

Fig1. Cholesterol side chain cleavage to generate the intermediate pregnenolone followed by its separate conversion to either progesterone or to 17αOH-progesterone. The cholesterol side chain cleavage enzyme (csc) carries out three distinct enzymatic steps, comprising two successive hydroxylations on C-20 and C-22 (shown in green) followed by scission of the C-20–C-22 carbon–carbon bond that releases as products pregnenolone and the rest of the steroid side chain as isocaproaldehyde. Pregnenolone, depending upon the cell type (adrenals, ovary, or testes) can ultimately be converted into aldosterone, cortisol, estradiol, or testosterone. The two immediate fates of prenenolone are its conversion either by the P450c17 enzyme into 17αOH-pregnenolone or by the 3βHSD2 enzyme into progesterone or 17αOH-progesterone. The 3βHSD2 enzyme carries out two distinct catalytic steps : first a dehydrogenation of the 3β-hydroxyl (shown in blue) followed by isomerization of the Δ5,Δ6 double bond to become a Δ4,Δ5 double bond (shown in blue) for both progesterone and 17αOH-progesterone.

The cholesterol side chain cleavage enzyme (P450scc) (reaction 1 in Table 1) carries out three successive enzymatic steps that are all physically associated with the inner mitochondrial membrane (IMM). These involve the separate 20R- and 22R-hydroxylations followed by cleavage of the side chain on the two carbons bearing the newly incorporated hydroxyl groups. Each of these steps is an oxidation reduction reaction requiring a pair of electrons, which is supplied by NADPH. The P450scc protein molecular weight is 49,000. The P450scc from the human adrenal and testes have identical sequences.

Table1. ^a Key Human Enzymes Concerned with the Production of Steroid Hormones

اخر الاخبار

اخبار العتبة العباسية المقدسة

قسم التطوير يبحث آفاق التعاون المشترك مع المعهد العالي لإعداد وتأهيل القادة

إدارة العتبة العباسية المقدسة تطلع على آليات تطوير المهارات الحِرَفية بقسم صناعة الشبابيك

سماحة السيد الصافي يؤكد أهمية التدريب المستمر وتطوير قدرات الملاكات الطبية للارتقاء بالخدمات الصحية

العتبة العباسية المقدسة تقيم مجلسًا عزائيًا لإحياء ذكرى شهادة الإمام الكاظم (عليه السلام)

المزيد

الآخبار الصحية

6 فواكة تساعدك على الشعور بتحسّن عند المرض

حفاظا على صحة العين.. هذا أفضل وقت لتناول فيتامين أ

الاستخدام اليومي لسماعات الأذن.. أخطر مما تتصور !

هل توقيت نشاطك اليومي يؤثر على صحة دماغك؟.. العلماء يجيبون

المزيد

الآخبار التكنلوجية

ابتكار ألماني قد يغيّر مستقبل صناعة البلاستيك

تحديثات وأرباح عبر المشاهدات.. ما الذي تخطط له "لينكد إن"؟

"الكوكايين الوردي".. مخدر جديد يثير قلق السلطات الأميركية

دراسة: تغيّرات في أسلوب القيادة قد تكشف مبكرا عن الخرف !

المزيد

مواضيع ذات صلة

Steroidogenic Acute Regulatory Protein (StAR)

Cytochrome P450 Steroid Hydroxylases

Major Protein Components of Muscle Fibers

The Major Components of Cartilage are Type II Collagen & Certain Proteoglycans

Bone is Affected by many Metabolic & Genetic Disorders

The Assembly of Membranes is Complex

Transport Vesicle Formation and Function Involves SNAREs & Other Factors

Misfolded Proteins Undergo Endoplasmic Reticulum Associated Degradation

Proteoglycans & Glycosaminoglycans

The ER Functions as The Quality Control Compartment of The Cell

Proteins Follow Several Routes to be Inserted Into or Attached to The Membranes of The Endoplasmic Reticulum

Proteins sorted via the Rough ER branch have N-Terminal signal peptides