1. Look up the tyr and trp content and molecular masses ofbovine serum albumin and chicken
lysozyme in the ExPASy Protein Knowledgebase
ExPASy Protein knowledgebase: http://www.uniprot.org
Search the Protein Knowledgebase (UniProtKB) for �bovine serumalbumin�. Select ALBU_BOVIN by clicking on accession P02769. Thensearch for �chick egg lysozyme� and select LYSC_CHICK by clickingon accession P00698. Scroll down each of these pages and you willcome to a section entitled "Sequence". This section gives thelength of the protein in amino acid residues, its molecular mass indaltons, and its sequence using one-letter abbreviations. Thesequence and molecular mass given for both BSA and chicken lysozymeare derived from the DNA sequence and therefore are of theunprocessed protein. This includes an N-terminal extension for bothproteins. To get the information about the processed protein,select �ProtParam� from the Tools function at the upper right ofthe protein sequence. Then click �GO�. This will take you to a newwindow with a list of regions of the protein that can be analyzed.Click on the numbers to the right of �CHAIN� (these numbers denotethe amino acid residues of the main chain. A new window will openthat shows only the amino acid sequence of the processed protein.Below the sequence you will find the molecular mass of theprocessed protein, listed as �molecular weight�, and a tableshowing the amino acid composition of the protein. You will findthe number of tyrosine and tryptophan resides listed on thistable.
2. Calculate ?mol tyr + trp / mg protein
for BSA and lysozyme.
3. Answer the following questions:
-
Should a standard curve for a Lowry protein assay using a BSAstandard look identical to
a standard curve based on lysozyme? Why or why not? A comparisonof the amino acid composition of these two proteins that you justcalculated will help you answer this question. If you believe thatthe curves will look different, be specific about how they will bedifferent.
Why would it be poor lab procedure to use a standard curve froma previous assay and run an assay only on the new unknown sampleswith fresh reagents? Name specific sources of error that this wouldcreate.
1. Look up the tyr and trp content and molecular masses ofbovine serum albumin and chicken
lysozyme in the ExPASy Protein Knowledgebase
ExPASy Protein knowledgebase: http://www.uniprot.org
Search the Protein Knowledgebase (UniProtKB) for �bovine serumalbumin�. Select ALBU_BOVIN by clicking on accession P02769. Thensearch for �chick egg lysozyme� and select LYSC_CHICK by clickingon accession P00698. Scroll down each of these pages and you willcome to a section entitled "Sequence". This section gives thelength of the protein in amino acid residues, its molecular mass indaltons, and its sequence using one-letter abbreviations. Thesequence and molecular mass given for both BSA and chicken lysozymeare derived from the DNA sequence and therefore are of theunprocessed protein. This includes an N-terminal extension for bothproteins. To get the information about the processed protein,select �ProtParam� from the Tools function at the upper right ofthe protein sequence. Then click �GO�. This will take you to a newwindow with a list of regions of the protein that can be analyzed.Click on the numbers to the right of �CHAIN� (these numbers denotethe amino acid residues of the main chain. A new window will openthat shows only the amino acid sequence of the processed protein.Below the sequence you will find the molecular mass of theprocessed protein, listed as �molecular weight�, and a tableshowing the amino acid composition of the protein. You will findthe number of tyrosine and tryptophan resides listed on thistable.
2. Calculate ?mol tyr + trp / mg protein
for BSA and lysozyme.
3. Answer the following questions:
-
Should a standard curve for a Lowry protein assay using a BSAstandard look identical to
a standard curve based on lysozyme? Why or why not? A comparisonof the amino acid composition of these two proteins that you justcalculated will help you answer this question. If you believe thatthe curves will look different, be specific about how they will bedifferent.
Why would it be poor lab procedure to use a standard curve froma previous assay and run an assay only on the new unknown sampleswith fresh reagents? Name specific sources of error that this wouldcreate.
