Question

You are to test the effectiveness and specificity of ninhydrin by spraying spots of water, the protein bovine serum albumin (BSA), and amino acids with ninhydrin. What do you predict the results will be, and why? What assumptions must you make?

Answer 1

Ninhydrin is the chemical which is used to detect the presence of Secondary and primary amines or ammonia.The color which appears the indication of these groups are purple or deep blue mostly in the cases where free amines are present in the compound or solution.

Being a organic compound , ninhydrin librated the co2 gas on reacting with free amino acid .

so, according to question water does not show any kind of reactivity with ninhydrin because it does not contain amino derivative.

In case of BSA protein which comes from cows it is the polypeptide chain of following amino acids:cysteine , aspartic acid , glutamic ,lysine, argenine in high content and tryptophan ,methionine in low content.therefore, the requirement for the ninhydrin test is the presence of free primary or secondary amines or in case of proteins if N-TERMINUS PROTEIN IS THE REQUIREMENT.

All amino acids gives the ninhydrin color test due to the presence of amino group(NH2) which is mandatory for the amino acid although different analysis is required like all amino acid hydrolysed and give the ninhydrin test except proline therefore some amino acid gives direct test and some are hydrolysed and give the test.

So assumption , we are taking in case of BSA protein that if protein is ended with N-terminal amino acid then only it will give the color test by ninhydrin solution.deep blue or purple.