Lecture 3 - Enzyme Kinetics III

Question 1

what inhibits pyruvate kinase and in what form of inhibition does it inhibit?

Answer 1

alanine non-competitively inhibits pyruvate kinase

Question 2

what is alanine?

Answer 2

alanine = a negative allosteric modulator

alanine is one product of a series of enzyme-catalysed reactions, the first step of high is catalysed by phosphenol kinase

Question 3

why does it make sense for the product of an enzymatic chain of reactions to inhibit one of the enzymes earlier in the chain?

Answer 3

?

Question 4

what do many enzymes require in order to regulate activity?

Answer 4

many require Cofactors which regulate activity

Question 5

Apoenzyme + Cofactor =

Answer 5

Holoenzyme

Question 6

what do cofactors often derive from?

Answer 6

cofactors often derive from vitamins

Question 7

what are cofactors referred to be when they are tightly bound to an enzyme?

Answer 7

prosthetic group

Question 8

are cofactors specific to certain enzymes?

Answer 8

no, the same cofactor can be used by many forms of enzymes

Question 9

what are the functions of vitamins: A, D, E & K?

Answer 9

A: roles in vision, growth & reproduction

D: regulation of calcium and phosphate metabolism

E: antioxidant

K: blood coagulation

Question 10

ascorbate:

Answer 10

essentially an antioxidant that rescues the prolly hydorxylase enzyme by reducing the ferric ion

Question 11

how does ascorbate function?

Answer 11

the enzyme prolly hydroxylase has tightly bound fe2+ ions within its structure which reacts with oxygen to form an oxidised iron complex (ferric ion) which inactivates the enzyme - to prevent this the ascorbate reduces the ferric ion

Question 12

what does ascorbate deficiency result in?

Answer 12

scurvy

Question 13

what do enzymes consist of?

Answer 13

multiple subunits and multiple active sites

Question 14

cooperativity binding in enzymes:

Answer 14

enzymes can bind two substrate molecules at different binding sites, binding at one site affects the affinity for the other

Question 15

(+) / ( - ) cooperativity:

Answer 15

• if the binding rate of the second substrate is increased, it’s called positive cooperativity

• if the binding rate of the second substrate is decreased, it’s called negative cooperativity.

Question 16

is there association between the regulatory and active sites?

Answer 16

no, the regulatory site is separate from the active site

Question 17

enzymes exist in two states:

Answer 17

tense and relaxed, binding of the effector influences further binding of substrate

Question 18

“allosteric modulation” ???

Question 19

hexokinase:

Answer 19

a highly regulated enzyme that catalyses [glucose + ATP → glucose-6-phosphate + ADP] at the beginning of glycolysis and its the rate limiting step

Question 20

how does hexokinase work?

Answer 20

works by induced fit: a conformational change in the enzyme occurs upon binding to its substrate

also, allosterically inhibited by product

Question 21

what mechanism does hexokinase catalyse?

Answer 21

the nucleophilic attack of phosphate by hydroxyl of glucose

Question 22

hexokinase and glucokinase:

Answer 22

• conduct the same reaction, but have different properties
• hexokinase is found in the brain and in skeletal muscle, and is a regulatory enzyme (inhibited by high concentrations of its product), also has higher affinity for glucose
• glucoskinase is found in in the liver, and is absent in the brain and muscle, it is non-regulatory and has a lower affinity for glucose
• the difference in the two means that the organs (muscle and brain) that need the most energy are getting it and that the liver (that doesn’t need that much) doesn’t get wasted energy

Question 23

where is -1K/M founds in an enzyme rate graph?

Answer 23

before the KM where the line passes the X-axis

Question 24

what is Ki?

Answer 24

affinity of the enzyme for the inhibitor

Question 25

[SECOND LAST SLIDE ON ENZYME KINETICS III PPT FOR ALL EQUATIONS NEED TO KNOW]