6.enzymes (b) princ

8/12/2019 6.Enzymes (B) Princ

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ENZYMES OF CLINICAL SIGNIFICANCE

Creatine Kinase (CK)

Characteristics

Its molecular weight is approximately 82,000.

It is a dimer comprised of two subuits

the !, or brai subuit, ad

the ", or muscle subuit),

#his results i three CK isoe$ymes.

i. CK%!! (CK&) isoe$yme , (brai type)

ii. CK%"! (CK2) isoe$yme, (hybrid type)

iii. CK%"" (CK') isoe$yme, (muscle type)

electrophoretic separatio

CK%!! will migrate fastest toward the aode ad is therefore called CK-1.

CK%!! is followed by CK%"! (CK%2), ad, fially, by

CK "" (CK%'which exhibits the slowest mobility (.

It is geerally associated with *#+ regeeratio i cotractile or trasport

systems. Its predomiat physiologic fuctio occurs i muscle cells, where

it is ioled i the storage of high eergy creatie phosphate.

-ery cotractio cycle of muscle results i creatie phosphate use.

#his is accompaied with the productio of *#+ by CK reactio

#his results i relatiely costat leels of muscle *#+.

#he reersible reactio cataly$ed by CK is show i -uatio &0%/.

Creatie *#+ CK creatie phosphate *1+

Tissue Source

Highest actiities are foud i

seletal muscle

heart muscle

brai tissue.
http://tissue.ck/http://tissue.ck/http://tissue.ck/


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Smalleruatities are foud i

idey

the bladder

prostate

gastroitestial tract

lier

pacreas

splee

uterus

placeta

thyroid

lug

.

Lactate Dehydrgenase

3actate dehydrogease (31) is a e$yme that cataly$es

the itercoersio of lactic ad pyruic acids. It is a hydroge%trasfer

e$yme that uses the coe$yme 4*1 .

#issue Source

31 is widely distributed i the body. 5igh actiities are foud i the

heart, lier, seletal muscle, idey, ad erythrocytes6 lesser amouts are

foud i the lug, smooth muscle, ad brai.

As!artate Amintrans"erase

*spartate amiotrasferase (*7#) is a e$yme belogig to the class of

trasferases. It is commoly referred to as a trasamilase ad is ioled

i the trasfer of a amio group betwee aspartate ad a%eto acids.

#he older termiology, serum glutamic%oxaloacetic trasamiase (7#, or

GOT), may also be used. +yridoxal phosphate fuctios as a coe$yme.

#he trasamiatio reactio is importat i itermediary metabolism

because of its fuctio i the sythesis ad degradatio of amio acids. #heetoacids formed by the reactio are ultimately oxidi$ed by the

tricarboxylic acid cycle to proide a source of eergy.

#issue Source


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reactios. #he ma:or differece betwee *C+ ad *3+ is the p5 of the

reactio. *C+ fuctios at a optimal p5 of approximately ;.0.

%iss&eSource

*C+ actiity is foud i the prostate, boe, lier, splee, idey, erythrocytes,ad platelets. #he prostate is the richest source, with may times the actiity

foud i other tissue.

'(Gl&tamyltrans"erase

'%lutamyltrasferase (#) is a e$yme ioled i the trasfer of

the ' %glutamyl residue from ' %glutamyl peptides to amio acids, 52,

ad other small peptides. I most biologic systems, glutathioe seres as

the 'glutamyl door.

#he specific physiologic fuctio of # has ot bee clearly

established, but it is suggested that # is ioled i peptide ad

protei sythesis, regulatio of tissue glutathioe leels, ad the trasport

of amio acids across cell membraes.

#issue Source

# actiity is foud primarily i tissue of the idey, brai, prostate,

pacreas, ad lier. Cliical applicatios of assay, howeer, are cofied

maily to ealuatio of lier ad biliary system disorders.

Amylase

*mylase (*"7) is a e$yme belogig to the class of hydrolases that

cataly$e the breadow of starch ad glycoge. 7tarch cosists of both

amylose ad amylopecti. *mylose is a log, ubrached chai of glucose

molecules, lied by < &%/ glycosidic bods6 amylopecti is a brached%

chai polysaccharide with < &%= liages at the brach poits. #he structure

of glycoge is similar to that of amylopecti but is more highly

brached.


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%iss&eSource

#he aciar cells of the pacreas ad the saliary glads are the ma:or tissue

sources of serum *"7. 3esser cocetratios are foud i seletal muscle ad

the small itestie ad fallopia tubes. *"7 is the smallest e$yme, with a

molecular weight of ;0,000%;;,000. !ecause of its small si$e, it is readilyfiltered by the real glomerulus ad also appears i the urie.

1igestio of starches begis i the mouth with the hydrolytic actio of

saliary *"7. 7aliary *"7 actiity, howeer, is of short duratio

because, o swallowig, it is iactiated by the acidity of the gastric

cotets. +acreatic *"7 the performs the ma:or digestie actio of

starches oce the polysaccharides reach the itestie.

Li!ase3ipase (3+7) is a e$yme that hydroly$es the ester liages of fats to

produce alcohols ad fatty acids. 7pecifically, 3+7 cataly$es the partial

hydrolysis of dietary triglycerides i the itestie to the 2%mooglyceride

itermediate, with the productio of log%chai fatty acids.

#he e$ymatic actiity of pacreatic 3+7 is specific for the fatty acid

residues at positios & ad ' of the triglyceride molecule, but substrate

must be a emulsio for actiity to occur. #he reactio rate is

accelerated by the presece of colipase ad a bile salt.

Tissue Source3+7 cocetratio is foud primarily i the pacreas, although it is also

preset i the stomach ad small itestie.

Gl&cse()($hs!hate Dehydrgenase

lucose%=%phosphate dehydrogease (%=%+1) is a oxidoreductase that

cataly$es the oxidatio of glucose =phosphate to =%phosphoglucoate or

the correspodig lactoe. #he reactio is importat as the first step i the

petose%phosphate shut of glucose metabolism with the ultimateproductio of 4*1+5.

Tissue Source

7ources of %=%+1 iclude the adreal cortex, splee, thymus, lymph

odes, lactatig mammary glad, ad erythrocytes. 3ittle actiity is

foud i ormal serum.

6.enzymes (b) princ

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