MadSci Network: Biochemistry

Re: Questions about Trypsin

Date: Sat Mar 28 20:32:21 2009
Posted By: Karin Crowhurst, Assistant Professor, Biochemistry
Area of science: Biochemistry
ID: 1237882967.Bc


Trypsin cleaves peptide bonds in ANY protein (including casein) that are found after either lysine or arginine amino acids. So, this means that trypsin will chop a protein like casein into very small pieces (assuming that it has a number of lysine and arginine amino acids in its primary sequence). Presumably trypsin will make milk translucent because it has broken down casein and other proteins into smaller pieces, which would make the milk less opaque.

So, I dont know how much detail you need on the inhibitors, so I will just say simply that soybeans contain lots of proteins, including an enzyme (called "Soybean Trypsin Inhibitor") that binds to trypsin and inihibits its action. So, if you eat too many soybeans they will affect your digestion of ALL foods. Soybeans are considered toxic in large quantities. I don't know how copper sulphate works to inhibit trypsin.

In terms of the molecular mass of trypsin, the reason you keeep seeing different masses is that there are a lot of different types of trypsin - i.e. if you get trypsin from human or from cow, those two proteins are different. They may have the same tertiary structure, but their primary sequences will be slightly different from each other, which results in small differences in mass. Just choose one trypsin and then you might want to mention in your report specifically which trypsin you are using for molecular weight. So, if 1% is 1g of trypsin in 100 mL solution, then it is 5/100 = 0.05 g trypsin in 5 mL solution. So, if you use the molecular weight of bovine trypsin (~23.3 kDa = 23300 g/mol), then it corresponds to 2.1E-06 moles of trypsin.

Hope this helps!

[Moderator's Note: We have some answers in our archives that discuss some modes by which copper ions can inhibit proteins, and proteases in specific. Take a look at answers 1170952921.Bc, 1108142071.Bc, 1171305594.Bc, and 963184462.Bc. -- Steve Mack]

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