Protein section 5

The study of the rates of enzyme catalysed reactions is called..

The simplest way to investigate reaction rate is to monitor [blank_start]increase[blank_end] in reaction product against time. This can be done at a variety of [blank_start]substrate[blank_end] concentrations and the initial velocity of the reaction determined. Eventually the reaction will reach a plateau when the reaction equilibrium has been attained. In reality enzyme kinetics is more readily understood if we only consider the [blank_start]forward[blank_end] reaction and we define V0 as the number of [blank_start]moles[blank_end] of product formed per second when the reaction is just beginning at t ~0

add labels to the enzyme kinetics equation

What are the preconditions of the enzyme kinetics equation

when is this equation useful?

Label the Michaelis-Menten Relationship

The Michaelis constant is a measure of the affinity of the enzyme for its substrate and is expressed as..

Kcat is...

A low KM means a low affinity of enzyme for substrate

How can you find Kcat?

kcat is the number of substrate molecules transformed per molecule of enzyme per second (units are s-1) or i.e...

Label each column

Enzymes are capable of working on a number of substrates, some better than others. The efficiency of these enzymes depends both on kcat and on KM.

The specificity constant is defined as..

The [blank_start]higher[blank_end] the kcat and [blank_start]the lower[blank_end] the KM the bigger the specificity constant. The best substrate for an enzyme will have the [blank_start]highest[blank_end] specificity constant. This constant also describe the [blank_start]catalytic[blank_end] efficiency of enzymes.

What is the name of this equation?

Label the Lineweaver plot

Inhibitors can also be very useful substances used as pharmaceuticals. Examples would be [blank_start]penicillin[blank_end] which inhibits the enzyme responsible for cell wall biosynthesis in certain bacteria [blank_start]and aspirin (methyl salicylate)[blank_end] which binds to and inhibits cyclooxygenase enzymes.

There are two types of inhibition, REVERSIBLE and IRREVERSIBLE. Reversible inhibition is said to be [blank_start]COMPETITIVE[blank_end] whereas irreversible inhibition [blank_start]can be NON-COMPETITIVE or UNCOMPETITIVE.[blank_end]

This inhibition is...

In competitive inhibition KM is [blank_start]increased[blank_end] but Vmax remains unaltered. An example of competitive inhibition is inhibition of succinate dehydrogenase by malonate. Malonate competes with succinate for [blank_start]binding[blank_end] at the active site but cannot be converted to fumerate. [blank_start]Increasing[blank_end] the concentration of succinate competes out the inhibitor.

This inhibition is...

In uncompetitive inhibition KM is [blank_start]unaltered or appears reduced[blank_end] and Vmax is [blank_start]dramatically reduced[blank_end] There is no requirement for the inhibitor to resemble the structure of the [blank_start]substrate[blank_end]. The inhibitor does not bind to free enzyme only to [blank_start]ES complexed[blank_end] enzyme. It is believed that these type of inhibitors distort the active site region [blank_start]preventing[blank_end] further substrate turnover.

This inhibition is..

A non-competitive inhibitor binds to both the free E and the ES complex and the effect of this is to [blank_start]lower[blank_end] the effective number of enzyme molecules. The rsult is [blank_start]a decrease[blank_end] in Vmax as a result of changes in [blank_start]kcat[blank_end]. Vmax is [blank_start]reduced[blank_end] and KM is not normally effected

What are the EXAMPLES OF IRREVERSIBLE ENZYME INHIBITORS