A quantitative amino acid analysis reveals that bovine serum...

A quantitative amino acid analysis reveals that bovine serum albumin (BSA) contains 0.58\% tryptophan $\left(M_{\mathrm{r}} 204\right)$ by weight. (a) Calculate the $minimum$ molecular weight of BSA (i.e., assume there is only one Trp residue per protein molecule). (b) Size-exclusion chromatography of BSA gives a molecular weight estimate of 70,000. How many Trp residues are present in a molecule of serum albumin?

A quantitative amino acid analysis reveals that bovine serum albumin (BSA) contains 0.58\% tryptophan $\left(M_{\mathrm{r}} 204\right)$ by weight.
(a) Calculate the $minimum$ molecular weight of BSA (i.e., assume there is only one Trp residue per protein molecule).
(b) Size-exclusion chromatography of BSA gives a molecular weight estimate of 70,000. How many Trp residues are present in a molecule of serum albumin?

Key Concepts

Size-Exclusion Chromatography

Size-exclusion chromatography is a laboratory technique used to separate molecules based on their size, which can be correlated to molecular weight. This method provides an experimental estimation of a protein’s molecular weight that can be compared to theoretical calculations derived from amino acid composition analysis.

Amino Acid Residue Count Calculation

This concept addresses the determination of the number of specific amino acid residues within a protein. By combining the estimated total molecular weight with the percentage composition, one can calculate the number of residues of a particular amino acid in the protein, reflecting the protein's compositional structure.

Percentage Composition Analysis

This concept involves using the weight percentage of a particular component within a complex mixture or macromolecule to deduce overall properties such as molecular weight. In the context of proteins, knowing the percentage weight of an amino acid can allow estimation of the protein's molecular weight, assuming a minimum number of that residue is present.

Molecular Weight Determination from Component Analysis

This refers to the method of calculating the total molecular weight of a compound based on the known mass and proportion of its constituents. For proteins, if the mass contribution of a specific amino acid residue is known, the overall molecular weight can be estimated by treating that residue's mass as a fraction of the protein’s total mass.

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