Talk:Structural Biochemistry/Protein function/Heme group/Hemoglobin/Affinity Constant

It would be helpful to note whether "stronger" affinity has a higher or lower numeric Ka. In research on vitamin D binding protein, for example, which is a "stronger" Ka: 1.12 10^-9 M or .36 10^-9 M? How about 1.0 10^-9 vs 1.0 10^-7 M. And what's the M stand for?