M.Prasad NaiduMSc Medical Biochemistry, Ph.D,.

Hemepurinespyrimidineshormonesneurotransmittersbiologically active peptides

Derived from beta-alanine and histidine

Anserine is formed by methylation of carnosineby S-adenosylmethione

(beta-alanine is derived from cytosine)

Carnosine and anserine occur in muscle andactivate myosin ATPase activity (myosin isthe chief enyzme involved in contraction ofmuscle)

Homocarnosine occurs in the brain.Homocarnosinosis is an extremelyrare disorder due to carnosinasedeficiency. It is associated withmental retardation

Decarboxylation of histidineforms histamine. Other compoundsarising from histidine are shown here

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.

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). Ornithinedecarboxylase has a half-life of 10 minutes.

Melatonin regulates circadian rhythms

Tyrosine hydroxylase

tryptophan

Serotonin is a potentvasoconstrictorand stimulator ofsmooth muscle contraction

Inhibition of MAO by iproniazidincreases effects of serotonin

Melanin polymers contain both eumelanin and pheomelanin in varying amounts.

Albinism accompanies defective melanin biosynthesis. Tyrosinehydroxylase-negative albinos lackall visual pigment

Creatine is a high-energy storage compound in muscle. ATP is made from creatine phosphate by creatine kinase

Porphyrias are a group of diseases caused byabnormalities in the pathway of biosynthesisof various porphyrins.

Examples of important porphyrins in nature arethe iron porphyrins such as the heme of hemoglobin,and the magnesium porphyrin in chlorophyll.

Usually, type III is formed but incertain porphyrias, the type Iisomers are formed in excess.

These compounds are not conjugateddue to the methylene groups. Oxidation is catalyzed by light leadingto formation of the colored porphyrins.

Porphyrins have a very strong absorbance due to extendedconjugation of double bonds.

Porphyrins are used in cancerphototherapy. Tumors oftentake up more porphyrins thannormal tissue. Lasers will excitethe porphyrin to a high energyintermediate that breaks down andresleases cytotoxic agents that kill the tumor.

Accumulation of porphyrinogenscan cause sensitivity to light leadingto skin damages

Mutations in in enzymes 2- 8cause the porphyrias. Regulation ofheme synthesis occurs at ALA synthaseby a repression-derepression mechanism mediated by heme. Thedotted lines indicate the negativeregulation by repression.