Chapter 22, Problem 18DAP

(a)

Summary Introduction

To describe: The chemical transformation which is required to convert glutamate to (2S)-4-amino-2-hydroxybutyrate (AHBA).

Introduction:

Glutamate comes under the category of non-essential amino acid and it contains two carboxyl groups. It is an acidic amino acid which is important part of the neurotransmission process. AHBA (4-amino-2-bydoxy butyrate) it is main component of many antibiotics.

Explanation of Solution

Pictorial representation: Fig.1 shows formation of AHBA from glutamate.

Fig.1: Formation of AHBA from glutamate.

Explanation:

AHBA (4-amino-2-bydoxy butyrate) is formed from the glutamate by the process of decarboxylation. When there is a removal of α-carboxyl group from the glutamate and addition of one –OH group to the γ-carbon then AHBA is formed which is given in Fig. 1.

(b)

Summary Introduction

To determine: How Btrl can act as an acyl carrier protein with a Coenzyme A prosthetic group.

Introduction:

Coenzyme A is important in the synthesis and oxidation of the fatty acids and it also help in the citric acid cycle during the oxidation of the pyruvate.

Explanation of Solution

Explanation:

Btrl and acyl carrier proteins have similarities in terms of their sequences. When this compound incubated in CoA conditions it increases its molecular weight. It is because CoA molecule can bind to Btrl molecule when CoA is added to the serine residue (any one) with the replacement of the hydroxyl group with a 4’-phosphopantertheine group

The molecular weight of the CoA is 17;

And the molecular weight of 4’phosphopantetheine is 356;

Molecular mass of purified Btrl protein is 11,812.

So, the overall molecular weight of the Btrl which could act as an acyl carrier protein with a Coenzyme A would be as follows:

$11,182-17+356=12,151$

This calculated molecular weight is very much close to the observed molecular weight 12,153.

Conclusion

Conclusion:

Btrl can act as an acyl carrier protein with a Coenzyme A because the expected molecular weight is very close to the calculated value of molecular weight which is 12,153.

(c)

Summary Introduction

To determine: The structures which are consistent with the proposed structure of γ-glutamyl-S-Btrl.

Introduction:

Alpha carboxyl group is any organic molecule group that contains basic amino group and acidic carboxyl group which is very unique to each amino acid.

Explanation of Solution

Pictorial representation: Fig. 2 shows glutamyl-S-Btrl.

Fig.2: Glutamyl-S-Btrl

Explanation:

One more structure which is consistent is that a thio-ester could formed with the α-carboxyl group which is represented in the Fig. 2. Thio-ester is the compound which has functional group R-S-CO-R’ and they are final products of esterification. In the given figure arrow represent the alpha carboxyl group and thio group in the structure of the Glutamyl-S-Btrl.

(d)

Summary Introduction

To determine: The chemical basis of the γ-glutamyl-S-Btrl can be correct because the alpha carboxyl group might be removed at some stage in the process.

Introduction:

Organic molecule group such as alpha carboxyl group that contains basic amino group and acidic carboxyl group and it is very unique to each amino acid.

Explanation of Solution

Explanation:

The process of removal of a carboxyl group from a compound is termed as decarboxylation. In many reactions, carboxyl group should be in a free state for an amino acid to be removed. It is very difficult to imagine that decarboxylation process can occur with a carboxyl group in its thio-ester form.

(e)

Summary Introduction

To determine: The most likely structure of the BtrK species

Introduction:

Decarboxylation is a chemical reaction in which carbon dioxide gets released.

Explanation of Solution

Pictorial representation: Fig 3 shows most likely structure of the BtrK

Fig 3: Most likely structure of the BtrK

Explanation:

The molecular species of M_r is 12,240 when the γ-glutymyl-S-Btrl is incubated with purified Btrl.

The molecular species of M_r is 12,281 of γ-glutymyl-S-Btrl.

Therefore,

$\begin{array}{l}\text{12,240}\text{-12,281}\\ \text{=}\text{41}\approx {\text{M}}_{\text{r}}\text{of}{\text{CO}}_{\text{2}}\end{array}$

Due to decarboxylation of the BtrK, carboxyl group would be deleted from the structure and only amine group and alpha carboxyl group and thio group will remain in the BtrK species as represented in the Fig. 3.

(f)

Summary Introduction

To determine: The molecular structure of the species whose molecular mass is 12,370.

Introduction:

A pure substance is made from molecules with the average geometrical structure. The chemical formula and the structure of a molecule are the two important factors that determine.

Explanation of Solution

Pictorial representations: Fig 4 shows expected molecular structure of the species whose molecular mass is 12,370.

Fig 4: Expected molecular structure of the species whose molecular mass is 12,370.

Explanation:

The Molecular structure of the species whose molecular mass is 12,370 is represented in the figure 4. The molecular species  of M_r is 12,240 when the γ-glutymyl-S-Btrl is incubated with purified Btrl. The Molecular structure of the species whose molecular mass is 12,370.

Therefore,

$\begin{array}{l}12,370-12,240\\ =130\end{array}$

This molecular structure would have free amino group and alpha carboxyl group and thio group will remain in the new species.

(g)

Summary Introduction

To propose: The plausible pathway for the synthesis of AHBA with the help of enzymes that catalyze each step and any kind of cofactors and substrate required during the pathway.

Introduction:

In the plausible pathways different kind of enzyme and cofactor and substrate are used with the help of these factors a useful product can be synthesized.

Explanation of Solution

Pictorial representation: Fig.5 shows the plausible pathway for t.he synthesis of AHBA

Fig.5: The plausible pathway for the synthesis of AHBA

Explanation:

The plausible pathway for the synthesis of AHBA and respective addition of antibiotics is represented in the Fig. 5. This pathway includes the involvement of co-factor such as ATP, NAD and glutamate amino acid.