You asked this question already and it was closed as off-topic. I'll leave this one for now and see what other people think.

This seems to be a purely biochemical property, therefore it makes more sense to read the wikipedia entry, a biochemistry book, or as in a biology forum than asking computational biologists. the tags however are not acceptable, please don't use numbers as tags!

Actually the wikipedia entry contains the formula you need, thereby sufficiently answering your question. closing it as off topic.