If calcium binds to proteins, then why doesn't it bind to the casein in milk?

Factual Questions
1

If calcium binds to proteins, then why doesn’t it bind to the casein in milk?

2

Well, I don’t recall the exact structure of casein off the top of my head (and I call myself a Doper!), but not all proteins will bind calcium. They require a calcium-binding domain - a specific structural component designed to, get this, bind calcium. As I said, I don’t recall whether casein has one or not. For that matter, why are you under the impression that casein doesn’t bind calcium?

3

I am under the impression that it doesn’t bind because everyone swears it’s a good source of calcium. I am assuming if it were bound, it wouldn’t be a good source.

4

The behavior of sturctures in their native form is not necessarily the same as their behavior in the digestive system. The purpose of digestion is to reduce complex molecules down to their simplest forms so that they can be absorbed by the lining of the digestive tract. This is an entirely different environment than anything found in nature.

5

Casein has 32 acidic amino acids, aspartate and glutamate, which can bind to Ca[sup]2+[/sup]. This poses no problem for digestion, because none of these binding sites are tight enough to prevent absorption by the body, nor robust enough to stand up to digestion.

6

http://www.nal.usda.gov/ttic/tektran/data/000012/79/0000127969.html

The caseins DO bind calcium, quite strongly, however once in the digestive tract, the bond is not strong enough to prevent release of calcium.

7

The fact that the casein is hacked to little bits in said digestive tract might have something to do with calcium availability, too.

8

So, the digestive tract can handle breaking these casein-calcium bonds but not other protein-calcium bonds, such as whey?

For instance, some protein I take occasionally (Designer) has whey and a normal form of calcium and Ca pantothenate. Will this bind and then get broken up, or just not bind at all, or bind and not break up?

Also, if you eat a steak and in the same meal some milk, will the calcium bind to the steak protein and the break apart, or just never bind at all, or bind and not break up?

How about drinking my whey protein shake with some soy milk, which is enriched with calcium carbonate? Or, for that matter, will the calcium in the soy milk bind with the protein and then break apart or never bind at all, or bind and never break up?

What about eggs and cheese? Tuna/chicken and spinach salad?

I just want to know how often I am consuming bound calcium that never gets broken apart by the digestive tract.

9

Exapno Mapcase said

I think that our digestive tracts ARE found in nature :wink: