Alanine Racemase Coenzyme Identification
The enzyme alanine racemase catalyzes the interconversion of L-amino acids and D-amino acids. Specifically, it converts L-Alanine to D-Alanine, a reaction crucial in bacterial cell wall synthesis and other metabolic pathways.
This type of amino acid racemization reaction requires a specific coenzyme that facilitates the abstraction of the alpha-proton and the subsequent stereochemical inversion.
Coenzyme Role in Racemization
- Pyridoxal phosphate (PLP): This is the essential coenzyme for alanine racemase. PLP forms a Schiff base intermediate with the amino acid substrate, stabilizing the carbanionic intermediate formed during proton abstraction. This mechanism allows for the racemization process.
- Thiamine pyrophosphate (TPP): Primarily involved in decarboxylation reactions and the transfer of aldehyde groups (e.g., in pyruvate dehydrogenase).
- Tetrahydrofolate (THF): Acts as a carrier of one-carbon units, essential for nucleotide and amino acid synthesis.
- Flavin mononucleotide (FMN): Involved in redox reactions as an electron acceptor/donor (e.g., in flavoproteins).
Based on the known mechanisms of these coenzymes, only Pyridoxal phosphate is utilized by alanine racemase for the conversion of L-Alanine to D-Alanine.
Important Questions from Structure and Function of Biomolecules
- Match the carbohydrates in Column I with the correct glycosidic linkages involved in Column II.
Column I Column II P. Amylose 1. $\beta$ ($1\to 4$) Q. Sucrose 2. $\alpha$ ($1\to 4$) R. Amylopectin 3. $\alpha 1\to \beta 2$ S. Cellulose 4. $\alpha$ ($1\to 4$), $\alpha$ ($1\to 6$) - Match the biomolecules in Column I with their function given in Column II
Column I Column II P. Lectins 1. Acts as ATP dependent pump to efflux out small molecules Q. P-glycoprotein 2. Targets lysosomal enzymes to their destination R. Digitoxigenin 3. Specific carbohydrate binding proteins S. Mannose 6-phosphate 4. Inhibits Na$^+$-K$^+$ pump - Correctly match the following Monosaccharides with their respective Epimers.
Monosaccharide Epimer P. D-mannose 1. C-3 epimer of D-glucose Q. D-allose 2. C-4 epimer of D-glucose R. D-galactose 3. C-4 epimer of D-mannose S. D-talose 4. C-2 epimer of D-glucose 5. C-5 epimer of D-glucose - Which of the following show(s) optical activity at 100 mM concentration in water?
An octapeptide composed of these L-amino acids – Lys, Thr, Ser, Met, Arg, Trp, Tyr, Glu was subjected to analyses with the following outcomes:
P. The N-terminal sequencing analysis by Sanger's method yielded 'Ser' at the N-terminus
Q. Chymotrypsin treatment gave a pentapeptide, a ‘Tyr' containing dipeptide and a free ‘Glu'
R. Cyanogen bromide treatment gave two tetrapeptides
S. Trypsin treatment gave two tripeptides and a dipeptide
Which one of the following is the correct octapeptide sequence?
