Here is the amino acid sequence for bovine casein, using the one letter amino ac

Question

Here is the amino acid sequence for bovine casein, using the one letter amino acid codes.

MKVLILACLVALALARELEELNVPGEIVESLSSSEESITRINKKIEKFQSEEQ
QQTEDELQDKIHPFAQTQSLVYPFPGPIPNSLPQNIPPLTQTPVVVPPFLQPE
VMGVSKVKEAMAPKHKEMPFPKYPVEPFTESQSLTLTDVENLHLPLPLLQSWM
HQPHQPLPPTVMFPPQSVLSLSQSKVLPVPQKAVPYPQRDMPIQAFLLYQEPV
LGPVRGPFPIIV

Put a box around any residues that will have a positively charged side chain at a pH equal
to the pI value that you determined.

Put a circle around any residues that will have a negatively charged side chain at a pH
equal to the pI value that you determined.

Is this sequence consistent with the pI value that you determined? Explain why or why not.

Explanation / Answer

pI = pKa1 + pKa2 / 2

For this protein, the pI value comes out to be 5.7

So, pH = 5.7

Lets calculate the net charge on the protein at this pH

Total positively charged residues = 4 (R) + 12 (K) = 16

Total negatively charged residues = [ - 4 (D)] + [- 19 (E)] = - 23

Therefore, net charge of protein = - 7

or protein is negatively charged

The isoelectric point (pI), is the pH at which a particular molecule carries no net electrical charge.

So, this sequence is not consistent with the pI value that was determined

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