23-07-2012, 09:17 AM
Good morning Karen,
It's actually you who found this:
http://www.jbc.org/content/265/11/6048.full.pdf
The chemical equilibrium constants that I referred to in the above posts are called "association constants" in that article. Think of a chemical reaction that forms some sort of association between DHT and SHBG, like a strong chemical bond or a loose complex:
DHT + SHBG ---> complex
The association constant is the ratio of the concentrations (or "levels", in pg/l or ng/dl) of the resulting complex to those of the parts that make it up:
[complex]
--------------- = Ka
[DHT].[SHBG]
The higher Ka, the more difficult the complex will fall apart. If you replace DHT by testosterone in this equation, you get a lower Ka. If you replace it by estrogens, Ka will become even lower. So at any given SHBG concentration, the percentage of total DHT that is free is very small. The percentage of testosterone that is free is bigger, and the percentage of estrogens that are free is even bigger than that. The numbers are in the linked article.
If you replace SHBG in the above equation by albumin, 5α-reductase, or aromatase, you get another pecking order, of which binds strongest to DHT. If you matrix all the hormones against all receptors and other proteins and enzymes, you can probably find literature to fill the whole matrix with numbers for Ka. Some authors use the dissociation constants: Kd = 1 / Ka.
Chemical equilibrium is a matter of percentages of free and bound hormones. It's not about which binds first. The discipline that looks into rates of chemical reactions is called kinetics. That's when you get into half lives, rate constants, etc.
It's actually you who found this:
http://www.jbc.org/content/265/11/6048.full.pdf
The chemical equilibrium constants that I referred to in the above posts are called "association constants" in that article. Think of a chemical reaction that forms some sort of association between DHT and SHBG, like a strong chemical bond or a loose complex:
DHT + SHBG ---> complex
The association constant is the ratio of the concentrations (or "levels", in pg/l or ng/dl) of the resulting complex to those of the parts that make it up:
[complex]
--------------- = Ka
[DHT].[SHBG]
The higher Ka, the more difficult the complex will fall apart. If you replace DHT by testosterone in this equation, you get a lower Ka. If you replace it by estrogens, Ka will become even lower. So at any given SHBG concentration, the percentage of total DHT that is free is very small. The percentage of testosterone that is free is bigger, and the percentage of estrogens that are free is even bigger than that. The numbers are in the linked article.
If you replace SHBG in the above equation by albumin, 5α-reductase, or aromatase, you get another pecking order, of which binds strongest to DHT. If you matrix all the hormones against all receptors and other proteins and enzymes, you can probably find literature to fill the whole matrix with numbers for Ka. Some authors use the dissociation constants: Kd = 1 / Ka.
Chemical equilibrium is a matter of percentages of free and bound hormones. It's not about which binds first. The discipline that looks into rates of chemical reactions is called kinetics. That's when you get into half lives, rate constants, etc.