I got streptavidin for surface reaction. The label says "biotin binding: 16 units/mg". What does units/mg
mean?
Does it mean "1 mg biotin can bind to 16 units SA"?
How much is the unit
here?
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Sign up to join this communityI got streptavidin for surface reaction. The label says "biotin binding: 16 units/mg". What does units/mg
mean?
Does it mean "1 mg biotin can bind to 16 units SA"?
How much is the unit
here?
16 units/mg means 16 units per milligram of protein.
Many companies, including Invitrogen, define 1 unit streptavidin as the amount of streptavidin necessary to bind 1 microgram of biotin.
16 units/mg
actually means 1 gram of SA could bind to 16 gram of biotin? How come this happen? The molecular weight of SA is hundred times larger than of biotin, is it possible to have thousands of binding position?
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units/mg
. You must find out how much 1 unit of biotin weigh to make a comparison. For example if one unit of biotin weighs 1/16 milligram then 1 mg SA will bind to 1 mg biotin.
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Just to add to Chris Stronk's answer:
1 U SAV can bind 1 ug biotin
This tells you that in a 16 U/mg SAV sample, every mg of SAV will bind 16 ug of biotin. You can figure out the molar ratio from this:
$16\mu g\ BIO\cdot\frac{1mol\ BIO}{244310000ug\ BIO}\cdot\frac{52800000mg\ SAV}{mol\ SAV}$
Which equals:
$\frac{3.46mol\ BIO}{mol\ SAV}$
Theoretically, each SAV tetramer can bind 4 biotins. This tells you that there is some heterogeneity in the sample and that, on average, each SAV tetramer can bind 3.46 biotins.