Conversion of amino acids to specialized products
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Conversion of Amino Acids toSpecialized Products

M.Prasad Naidu

MSc Medical Biochemistry, Ph.D,.

Conversion of Amino Acids toSpecialized Products






biologically active peptides

Formation of glycine conjugates

Compounds related to histidine

Decarboxylation of histidine

forms histamine. Other compounds

arising from histidine are shown here

(beta-alanine is derived from cytosine)

Derived from beta-alanine and histidine

Anserine is formed by methylation of carnosine

by S-adenosylmethione

Carnosine and anserine occur in muscle and

activate myosin ATPase activity (myosin is

the chief enyzme involved in contraction of


Homocarnosine occurs in the brain.

Homocarnosinosis is an extremely

rare disorder due to carnosinase

deficiency. It is associated with

mental retardation

Arginine, ornithine, and proline metabolism

Structures of natural polyamines

Spermidine and spermine function in diverse physiologic processes that share as a common thread

a close relationship to cell proliferation and growth.

The fact that they are polycations allows these compounds to bind to DNA and RNA

and they are involved in packaging of DNA in bacteriophages.

Biosynthesis of spermidine and spermine

Addition of inhibitors of ornithine decarboxylase,

the enzyme that catalyzes the initial reaction in

polyamine biosynthesis, triggers overproduction

of ornithine decarboxylase. (hence, the machinery

that makes the protein is regulated tightly in order

that a supply of the precursors to spermidine and

spermine is always available). Ornithine

decarboxylase has a half-life of 10 minutes.

Catabolism of polyamines


Biosynthesis andmetabolism ofmelatonin



Melatonin regulates

circadian rhythms

Serotonin is a potent


and stimulator of

smooth muscle contraction

Inhibition of MAO by iproniazid

increases effects of serotonin

Eumelanin and pheomelanin biosynthesis

Melanin polymers contain both

eumelanin and pheomelanin in

varying amounts.

Albinism accompanies defective

melanin biosynthesis. Tyrosine

hydroxylase-negative albinos lack

all visual pigment

Biosynthesis of epinephrine and norepinephrine

Biosynthesis of creatine and creatinine

Creatine is a high-energy storage compound in muscle. ATP is

made from creatine phosphate by creatine kinase

Metabolism of -aminobutyrate


Porphyrias are a group of diseases caused by

abnormalities in the pathway of biosynthesis

of various porphyrins.

Examples of important porphyrins in nature are

the iron porphyrins such as the heme of hemoglobin,

and the magnesium porphyrin in chlorophyll.


Uroporphyrins and coproporphyrins

Biosynthesis of porphobilinogen

Conversion of porphobilinogen to uroporphyrinogens

Usually, type III is formed but in

certain porphyrias, the type I

isomers are formed in excess.

These compounds are not conjugated

due to the methylene groups.

Oxidation is catalyzed by light leading

to formation of the colored porphyrins.

Decarboxylation of uroporphyrinogens

Biosynthesis of porphyrin derivatives

Addition of iron to protoporphyrin

Absorption spectrum of hematoporphyrin

Porphyrins have a very strong

absorbance due to extended

conjugation of double bonds.

Porphyrins are used in cancer

phototherapy. Tumors often

take up more porphyrins than

normal tissue. Lasers will excite

the porphyrin to a high energy

intermediate that breaks down and

resleases cytotoxic agents that kill

the tumor.

Accumulation of porphyrinogens

can cause sensitivity to light leading

to skin damages

Intermediates, enzymes, and regulation of heme synthesis

Mutations in in enzymes 2- 8

cause the porphyrias. Regulation of

heme synthesis occurs at ALA synthase

by a repression-derepression

mechanism mediated by heme. The

dotted lines indicate the negative

regulation by repression.

Biochemical causes of the major signs and symptoms of the porphyrias

Summary of major findings in the porphyrias

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