Pathway of biosynthesis

Knowledge of the biochemistry of the porphyrins and of heme is basic to understanding the varied functions of hemoproteins (see below) in the body. The porphyrias are a group of diseases caused by abnormalities in the pathway of biosynthesis of the various porphyrins. Although porphyrias are not very prevalent, physicians must be aware of them. A much more prevalent clinical condition is jaundice, due to elevation of bilirubin in the plasma. This elevation is due to overproduction of bilirubin or to failure of its excretion and is seen in numerous diseases ranging from hemolytic anemias to viral hepatitis and to cancer of the pancreas. 

The porphyrias are a group of disorders due to abnormalities in the pathway of biosynthesis of heme they can be genetic or acquired. They are not prevalent, but it is important to consider them in certain circumstances (eg, in the differential diagnosis of abdominal... 

Figure 47-7. Pathway of biosynthesis of dolichol-P-P-oligosaccharide. The specific linkages formed are indicated in Figure 47-8. Note that the first five internal mannose residues are donated by GDP-mannose, whereas the more external mannose residues and the glucose residues are donated by dolichol-P-mannose and dolichol-P-glucose. (UDP, uridine diphosphate Dol, dolichol P, phosphate UMP, uridine monophosphate GDP, guanosine diphosphate M, mannose G, glucose.)...

The preparation of antibodies specific for the individual plasma proteins has greatly facilitated their smdy, allowing the precipitation and isolation of pure proteins from the complex mixmre present in tissues or plasma. In addition, the use of isotopes has made possible the determination of their pathways of biosynthesis and of their turnover rates in plasma. 

Phenylpropanamide (130), from the aposematic beetle (genus Metrior-rhynchus) (Table VIII), has been purified by gas chromatography from the methanol extract. Its structure is presumed from mass spectral data and was confirmed by comparison with a synthetic sample (97). The co-occurrence of amide 130 and l-methyl-2-quinolone (57) in this beetle suggests a common pathway of biosynthesis and that they may be derived from the amino acid phenylalanine. 

Biotin 0.15-0.3 mg/day. The discovery that biotin deficiency in young chickens can lead to sudden death resulted in a recommendation to supplement infant formulations with biotin.3 Desthiobiotin, in which the sulfur has been removed and replaced by two hydrogen atoms, can replace biotin in some organisms and appears to lie on one pathway of biosynthesis. b/C Oxybiotin, in which the sulfur has been replaced by oxygen, is active for many organisms and partially active for others. No evidence for conversion to biotin itself has been reported, and oxybiotin may function satisfactorily in at least some enzymes. 

Less frequently NADPH is used to reduce an isolated double bond. An example is the hydrogenation of desmosterol by NADPH (Eq. 15-11), the final step in one of the pathways of biosynthesis of cholesterol (Fig. 22-7). In this and in other reactions of the same... 

Figure 24-25 Pathways of biosynthesis (green arrows) and catabolism of cysteine as well as other aspects of sulfur metabolism. Solid arrows are major biosynthetic pathways. The dashed arrows represent more specialized pathways they also show processes occurring in the animal body to convert methionine to cysteine and to degrade the latter.

Figure 25-4 Pathways of biosynthesis of ubiquinones, plastoquinones, tocopherols, and vitamin K.

Biosynthesis of the most common constituent of the bacterial-lipopolysac-charide core, L-glycero-D-manno-heptose, was shown239,240 to occur through enzymic epimerization at C-6 of the heptosyl group in 9. Genetic evidence241,242 supports this pathway of biosynthesis. 

P. M. Rubtsov and I. S. Kulaev (1977). Some pathways of biosynthesis and breakdown of polyphosphates in the green algae Acetabularia mediterranea. Biokhimiya (Moscow), 42, 1083-1089. 

The pathway of biosynthesis of steroids in the adrenal cortex 1.5.1. The enzymes of steroidogenesis... 

Fig. 2. Pathway of biosynthesis of the glucocorticoid, cortisol, in the adrenal cortex. Cholesterol, from stores in cholesteryl esters or from other sources (see text) is converted via mitochondrial cytochrome P-450SCC (cholesterol side-chain cleavage enzyme) to pregnenolone, which then is successively converted by the microsomal enzymes cytochrome P-450,7 (17a-hydroxylase), 3 j8-hydroxysteroid dehydrogenase/ isomerase and cytochrome P-450c2, (21-hydroxylase) to 11-deoxycortisol, followed by conversion by the mitochondrial cytochrome P-450ll(3 (11/3-hydroxylase) to cortisol. The short-term action of ACTH in stimulation of steroidogenesis is to increase the availability of cholesterol for conversion by cytochrome P-450scc. From Ref. 9.

The importance of elucidation of pathways of biosynthesis which regulate pheromone production is exemplified by the identification of additional pheromone components for the cabbage looper moth. 

Fig. 8.—Pathway of Biosynthesis of Some Sugar Nucleotides That Function as Gly-cosyl Donors for Biosynthesis of Glycoproteins and Glycoenzymes. (The heavy arrows indicate the sites of feedback control of the reactions.135)...

Figure 2. The pathway of biosynthesis of myo-inositol to free inositol by synthase reaction in mammalian tissues. This is a postulated intermediate presumed to occur during the course of the reaction. Crystallographic studies with yeast synthase support the presence of this intermediate.

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