Unit 4 Enzymes and electrolytes

Michaelis-Menten curve

describes the relationship

between

⚬ substrate concentration

⚬ and rxn velocity

V

velocity of reaction

Vmax

maximum velocity

⚬ occurs at enzyme saturation

⚬ must have excess substrate

[S]

substrate concentration

K

= Michaelis-Menten constant

⚬ = [S] at ½ V

⚬ unique to E w/ specific S

⚬ = E-S affinity

￭ lower affinity, higher K

First order kinetics

⚬ velocity directly proportional

to the substrate concentration

Zero order kinetics

velocity plateau

⚬ velocity is independent of

substrate concentration

reaction velocity over substrate conc

product/time

oxidoreductases

catalyze oxidation-reduction reactions between 2 substrates

￭ i.e. lactate dehydrogenase

transferases

⚬ catalyze the transfer of a group other than hydrogen between 2

substrates

￭ i.e. creatine kinase

hydrolases

⚬ catalyze hydrolytic cleavage of substrate

￭ i.e. lipase, amylase

high specificity

found predominately in one tissue

moderate specificity

widely distributed in the body

low specificity

found in most body tissues

LDH (LD) - lactate dehydrogenase

oxidoreductase involved in anaerobic

glycolysis

• found in most cells of the body

total increase or relative increase of one isoenzyme

Heart stuff too

⚬ highest found in:

￭ pernicious anemia

￭ megaloblastic anemia

LDH (LD) - lactate dehydrogenase measurement

lactate to pyruvate, yielding NADH

￭ increase in absorbance at 340 nm

ref range: 100 - 224 U/L

CK - creatine kinase

transferase involved in ATP regeneration in

muscle cells

• allows phosphate to be stored for energy as

creatine phosphate

highest amount found in:

⚬ skeletal muscle

⚬ brain

⚬ heart

CK - creatine kinase

measurements of isoenzymes used in

diagnosis of specific conditions

⚬ dimer with 2 subunits

￭ CK - MB

• cardiac muscle

CK - creatine kinase reaction

reverse reaction is most commonly used

⚬ coupled with hexokinase - G6PD - NADPH system

⚬ measure increased absorbance at 340nm as NADPH is formed

CK - creatine kinase reference range

AST (SGOT) - aspartate aminotransferase

transferase - transfer of an amino group between aspartate and -keto acids

• important in the synthesis and degradation of amino acids

• highest amount found in:

⚬ liver - highest in acute hepatocellular disorders

AST (SGOT) - aspartate aminotransferase measurement

decrease in absorbance at 340 nm

reference range= 5-35 U/L

AST (SGOT) - aspartate aminotransferase

transferase - transfer of an amino group between aspartate and -keto acids

• important in the synthesis and degradation of amino acids

• highest amount found in:

⚬ liver - highest in acute hepatocellular disorders

AST (SGOT) - aspartate aminotransferase significance

decrease in absorbance at 340 nm

• reference range

⚬ 5-35 U/L

The highest amount found in:

⚬ liver - highest in acute hepatocellular disorders

ALT (SGPT) - alanine aminotransferase

catalyzes transfer of amino group from alanine to -ketoglutarate

• highest amount found in:

⚬ liver

￭ MORE SPECIFIC THAN AST

ALT (SGPT) - alanine aminotransferase measurement

measurement

⚬ decrease in absorbance at 340 nm

• reference range

⚬ 7 - 45 U/L

ALP - alkaline phosphatase

frees inorganic phosphate from organic phosphate, yielding alcohol

• found in almost all tissues

• highest amount found in:

⚬ bone - osteoblast involvment = higher ALP

⚬ liver

ALP - alkaline phosphatase measurements

GGT - gamma-glutamyltransferase

transferase involved in

⚬ protein synthesis

⚬ regulation of tissue glutathione

⚬ transport of amino acids across membranes

• found in:

⚬ liver

other places too

• elevated in

⚬ alcoholism

GGT - gamma-glutamyltransferase measurement

• measurement

⚬ increased absorbance at 405 nm

• reference range

⚬ male: 6 - 55 U/L

⚬ female: 5 - 38 U/L

AMY - amylase

hydrolase involved in the digestion of starch

• secreted by:

⚬ salivary glands

⚬ pancreas

• useful in diagnosis of pancreatitis

• elevated in:

⚬ gastric and duodenal ulcers

⚬ renal disease

⚬ narcotic use

⚬ mumps

AMY - amylase measurement

measurement

⚬ synthetic carbohydrate hydrolyzed by amylase, product produces color change measured

spectrophotometrically

• reference range

⚬ serum 30 - 220 U/L

(LPS) Lipase

catalyzes the hydrolysis of tryglycerides, primarily sourced from pancreas

• elevated in:

⚬ acute pancreatitis

(LPS) Lipase measurement

measurement

⚬ synthetic lipid substrate, measure the rate of color formation spectrophotometrically

• reference range

⚬ < 38 U/L