Enzymes Flashcards
Competitive Inhibitors
Bind free enzyme at active site
Noncompetitive Inhibitors
Binds somewhere other than the active site
Uncompetitive Inhibitor
Binds to substrate
Zero-Order Kinetics (Enzymes)
Large excess of substrate so that the amount of enzyme is the only rate limiting factor
Total CK
Creatine Kinase
Increased in muscle, brain, or cardiac damage (CK-MB higher than 6% of total CK suggests MI)
CK Isoenzymes
Two subunits, M and B
CK1: CK-BB (Brain, GI, Prostate, Uterus)
CK2: CK-MB (Cardiac)
CK3: CK-MM (Cardiac, skeletal muscle)
LD Implications
Lactate Dehydrogenase
Increased in MI, Liver disease, Muscle trauma, renal infarction, Hemolytic diseases, Pernicious Anemia
LD Testing Methods
Spectrophotometry
LD converts NAHD to NAD while converting pyruvate to lactate
LD Isoenzymes
M and H chains, 4 subunits, 5 forms total
LD-1 and LD-2 are assoc. with Acute MI and erythrocyte destruction
LD-3: plumonary disorders, pancreatitis, amd lymphocystosis
LD-4 and LD-5 assoc. with Liver and Skeletal Muscle Disorders
AST
Aspartate transaminase, found in many tissues
Highest values found in Hepatitis
Increased in MI, liver disease, muscle trauma, renal infarction, hemolysis
ALT
Alanine transaminase
Highest values found in Hepatitis
Increased in liver disease, more liver specific
GGT
Increased in hepatobiliary disease (especially intra- and posthepatic biliary tract obstruction), or immediately after alcohol intake
Measured spectrophotometrically
ALP
Alkaline phosphatase
Optimum pH is 10, activates Mg2+
Isoenzymes are separated by electrophoresis: Regan, Placental, Intestinal, L-phenylalanine, Liver, Bone
Increased in Disorders of Bone, Hepatic Biliary Tree (highest)
Amylase
In Salivary and Pancreatic Glands
Needs Ca and Cl (Should be diluted with Saline, not water)
Only enzyme normally excreted in urine
Increased: acute pancreatitis, Mumps, peptic ulcer perforation, intestinal obstruction, cholecystitis, ruptured ectopic pregnancy, mesenteric infarction, acute appendicitis
Amylase measurement methods
Amyloclastic: measuring the disappearance of starch substrate
Saccharogenic: measures enzymatic action by sugar reduction
Chromolytic: measure absorbance of dye split from substrate
Enzymatic: defined substrate using coupled enzymatic reactions; can have interference from lipemia
Lipase
Found in Pancreas
Elevated in Pancreatitis
Measured turbidimetrically
ACP
Acid Phosphatase
Primarily from Prostate - highest elevation seen in metastasizing carcinoma of Prostate
Measured spectrophotometrically using a phosphate substrate
Specimens must be refrigerated and serum should be separated from cells as soon as possible
Cholinesterase
Erythrocyte acetylcholinesterase (AChE) - True cholinesterase Plasma acylcholine acylhydrolase (PChE) - pseudocholinesterase Destroys acetylcholine after nerve impulse transmission Causes of Lowered pseudocholinesterase: organophosphate poisoning, genetic susceptibility to certain anesthetics, hepatocellular disease
CK2
Immunoassays measure concentration
Rises in 6-10hours, peaks in 24, drops to normal in 2-3 days
Isoenzymes
Different forms of the same enzyme that perform the same catalytic function
Cofactor
A non-protein compound required for enzyme activity
Activators
Inorganic cofactors needed for enzymatic activity
Coenzyme
Organic cofactor such as NAD
Factors Influencing Enzymatic Reactions
Substrate concentration
Enzyme concentration
pH
Temp.
Inhibitors (Competitive, Noncompetitive, Uncompetitive)
pH and Temp. must remain constant for enzyme testing
Enzyme Measurement Endpoint Methods
Endpoint: Reaction stops at a specified time, the product made in that time is measured
Kinetic: Measures change in absorpance at timed intervals to observe the enzyme activity
G6PD
Mainly found in erythrocytes
Deficiency: inherited as X-linked trait, causing intravascular hemolysis when given anti-malarial drugs or fava beans
