Polypeptide chains that differ in sequence but have similar enzymatic activity
Isozymes/ isoenzymes
Accelerates the rate of chemical reaction
Catalyst
Are protein catalysts utilized by essentially all mammalian cells in specific biochemical reactions
Enzymes
Catalysis on an insoluble surface
Heterogenous catalysis
Defines the capacity of protein catalysts to recognize and bind only one or a few molecules, the substrate excluding all others
Binding/ enzyme specificity
A substrate binding to an active site where it exhibits preformed steric and electronic complementarity to the shape and charge distribution of the substrate. No shape changes necessary for optimal binding
Lock and key model
Model that postulates an initial weak, flexible interaction of the substrate with groups in the enzymes ES binding site. It triggers a conformational rearrangement of the enzymes surface to enhance binding affinity
Induced fit model
Each enzyme has two names:
Practical/ trivial (e.g. Trypsin and papain)
Systemic name - unique numeric code designation and the nature of catalytic reaction
Identify the class described by its type of reaction catalyzed:
Oxidation- reduction reactions
Oxidoreductases
Identify the class described by its type of reaction catalyzed:
Transfer of functional groups
Transferases
Identify the class described by its type of reaction catalyzed:
Hydrolysis reactions
Hydrolases
Identify the class described by its type of reaction catalyzed:
Group elimination to form double bonds
Lyases
Identify the class described by its type of reaction catalyzed:
Isomerizations
Isomerases
Identify the class described by its type of reaction catalyzed:
Bond formation coupled with ATP hydrolysis
Ligases
Identify enzyme:
Catalyze transfer of phosphate group between phosphate and ADP to form creatine+ATP
Cofactor: magnesium
Creatine phosphokinase (CPK)
Primary tissue sources of which CK:
Plasma
CK-MM with
Primary tissue sources of which CK:
Brain, smooth muscle, prostate, thyroid, gut and lungs
CK-BB
Primary tissue sources of which CK:
Cardiac muscles
CK-MB (20-30%), CK-MM (70-80%)
Primary tissue sources of which CK:
Skeletal muscle
CK-MB, CK-MM (mostly)
Diagnostic application (CK):
Released during ischemia, injury, inflammation
increased in chronic myopathies, chronic renal failure, acute respiratory exertion
CK-MM
Diagnostic application (CK):
Indicated for brain trauma/ surgery, injury to smooth muscles, pts with malignancy: prostate CA, small cell lung CA, intestinal malignancies, transient increase after MI
CK-BB
Diagnostic application (CK):
Most commonly requested for detection of acute MI
Following MI: it rises proportional to extent of infarction
Appears in serum within 6 hrs after acute MI
Peak value: 12-24 hrs
Duration: 1.5 - 3 days
CK-MB
Normal values of total serum CK:
24-170 U/L for women
24-195 U/L for men
Marked total serum CK (> = 5x normal) can be seen in pts with:
Trauma (electrocution, surgery)
Athletic individuals (released during strenuous activities)
Muscular dystrophy
Chronic inflammation of muscle
Mild/ moderate total serum CK (2 - 4x normal) can be seen in pts with:
Hyper or hypothermia
Hypothyroidism
After normal vaginal delivery
Reye’s syndrome
Forms that migrate electrophoretically in positions different from standard ones
Atypical isoenzymes
Catalyze formation of ATP and AMP from ADP
Released from Erythrocyes
Adenylate kinase
Complex of CK-BB with antibody (IgG)
Macro CK Type 1
Oligometric variant of CK; mitochondrial
(+) in serum - poor prognostic sign seen in pts with malignancies
Macro CK type 2
Digestive enzyme that acts extracellularly to cleave starch into smaller groups and to monosaccharides
Major sources: salivary glands, exocrine pancreas
Amylase (diastase)
It is:
Secreted by pancreozymin
Readily cleared in urine
Enters the duodenum at ampulla of vater via sphincter of oddi
Liw levels found in fallopian tube, adipose tissues, skeletal muscle, small intestine
Pancreatic amylase
In acute pancreatitis, serum amylase levels rise within ________; remains high for a few days; return to normal in _______ days
Rise within 6-24 hours
Returns to normal in 2 -7 days
In a normal serum amylase with suspicion of pancreatitis measure:
24 hour urine amylase or serum lipase
Constrict pancreatic duct sphincter, decrease intestinal excretion and increased absorption in the circulation
Morphine administration
Optimal pH of 5.0
Common to tissues esp. prostate
Small amounts in rbc, platelet, liver, spleen
Acid phosphatase (ACP)
Highly specific for prostatic ACP
Thymolphthalein monophosphate
Is measured typically by its ability to cleave phosphate groups at an acid pH.
Used for diagnosis or monitoring of prostatic adenocarcinoma
Total ACP/ acid phosphate
Major applications of ACP:
Evaluation of prostate CA - not elevated in CA confined within prostate, BPH, prostatitis or ischemia of prostate
Medico Legal evaluation in rape - vagina with little or no ACP, +ACP d/t seminal fluid
Widely distributed along the surface membranes of metabolically active cell
Type of hydrolase
Its most abundant isoforms are coded by a single gene on chromosome 1
Alkaline phosphatase
ALP has very high activity in:
Bones, liver, placenta, intestines, kidneys and WBC
Has been used to separate at least 6 different isoforms of ALP in healthy individuals
HPLC using weak anion exchange columns
Easiest and most common method for distinguishing ALP iso enzymes
Heat serum at 53C for 15 minutes then compare with unheated sample
Heat fraction
Bone ALP - extremely labile 10-20% retain original activity
Liver and placental ALP - heat stable liver 30 - 50% retained
Placenta will all retained
Chemical inhibitors of ALP:
Blocks placental ALP
Blocks liver and bone ALP
Urea - placenta
Phenylalanine - liver and bone ALP
Small,for the heart
Functions in storage and transfer of oxygen from hemoglobin in the circulation to intracellular respiratory enzymes of contractile cells
Myoglobin
True or false: myoglobin is one of the first to diffuse out of ischemic muscle cells before CK?
True
Binds tropomyosin; governs excitation contraction coupling
Troponins
90% sensitivity for MI 8 hrs after onset of symptoms
95% specificity for MI
36% specificity to unstable angina
Troponin I
84% sensitivity for MI 8 hrs after onset of symptoms
81% specificity for MI
22% specificity to unstable angina
Troponin T
Have unique forms expressed in myocardial cells but not in other muscle types -presence in serum highly specific for Myocardial injury
Troponin I and troponin T
Troponin is released in two phases:
- Initial damage (acute MI) peaks at 4-8 hours
2. Sustained release from intracellular contractile apparatus - occurs up to days after acute event
General advantages of troponin T and I:
- Released only ff cardiac damage
- Present, remain elevated for a long time:
troponin I is detectable up to 5 days
Troponin T 7 to 10 days ff IM
3.very sensitive - measured by immunoassay
Catalyze conversion of lactate to pyruvate using NAD as co factor
Present in cytoplasm of cells and all tissues in the body
Lactate dehydrogenase
Normal pattern of LD:
LD2>LD1>LD3>LD4>LD5
LD isozymes:
High in the heart, RBC and kidneys
LD1 and LD2
LD isoenzymes:
High in skeletal muscle and liver
LD4 and LD5
LD activity can be measured either the:
Forward (lactate to pyruvate) or the reverse (pyruvate to lactate)
Diagnostic applications of LD:
Markedly increased LD with normal AST, ALT and CK
Damage to biochemical dimple cells (RBC, WBC), kidney, lung, tumors
Diagnostic applications of LD:
Increased LD and CK; increased AST > ALT
Cardiac or skeletal muscle injury
Diagnostic applications of LD:
Increased AST snd ALT > LD
Transiently in liver disease
Used to confirm diagnosis of MI when CK isoenzyme analysis equivocal or after total CL and CK MB release has returned to normal
LD
Peak 48-72 hours
Returns to normal after 8 to 10 days
Used to estimate tumor mass including metastases
Total LD
LD1 or LD2 increase in germ cell tumors ( tumor markers)
Flip LD1/LD2 ratio:
Extreme exercise Acute MI Hemolytic anemia Megaloblastic anemia Renal cortical disease (renal infarct)
Isomorphic pattern - Increased total LD, normal isoenzymes with tombstone pattern will lead to:
Diffuse tissue damage accompanied by shock and hypoxemia
Increased LD 2,3,4
Malignancy and tumor burden
Increased LD 3,4; decreased LD 1,2:
WBC tumors, pulmonary disease
Increased LD 4,5
Skeletal muscle injury, ischemic toxic hepatic injury