Question on coagulation cascade - (Jan/02/2010 )

I have been looking at a number of sources regarding the contact activation form of the coagulation cascade, and I have seen conflicting information. I am hoping somebody that knows this area very well can settle my question once and for all.

In human blood coagulation Factor XII is converted to XIIa in a calcium-independent process, and Factor XIa, in the presence of Ca++ activates Factor IX.

What I am confused about is whether the conversion of XI to XIa is calcium-dependent or calcium-independent. Most of the references I have consulted have not mentioned Ca dependence, but I found one chart that showed that XI to XIa was dependent. Was that a typo on the chart?

No. Chart is correct. Ca dependant.