Question

A.) Functioning as nucleophile, which attacks the electrophilic carbonyl center of substrate

What is the function of cysteine residue in the active site of the following enzyme catalyzed reaction? CHZOPO NAD+ HCOH NADH CH OPC НСОН Ho Cys

B.) Functioning as electrophile, which attacks the nucleophilic carbonyl center of substrate

C.) Functioning as an acid

D.) Functioning as a base

The image is an example of:

A.) covalent catalysis

B.) acid-base catalysis

C.) metal-ion catalysis

D.) hydration catalysis

Answer 1

1. The cysteine residue act as nucleophile as it attack on Carbon of carbonyl as carbon contain partial positive charge and S of cysteine contain negative charge . This will result in removal of H- ion. So Option A will be correct.

2. The reaction is an covalent catalysis . Here NAD+ accept H- ion and from nucleophilic attack of cysteine acyl cysteine is formed. As In covalent catalysis bond between substrate and residue of enzyme is formed during catalytically cycle.