What is Thrombokinase?

Does anyone remember using the term “thrombokinase?” Kathryn Doig, PhD, Dean of the Michigan State University College of Natural Sciences, and Professor ofBiomedical Laboratory Diagnostics writes:

Hi George. We have a grad student who is doing a project related to hemostasis. Along the way,  she used the term “thrombokinase” which I had not heard in quite some time. Seems outdated to me, having been coined by Morawitz, I think. But just thought I would verify that it is not used anymore. KD

Here’s my response to Dr. Doig: Hi, Kathy. Factor X was first described in the 1950s as the Stuart factor and the Prower factor, named for the families in which the factor’s absence caused bleeding. Some time after, activated factor X was named “prothrombinase” because its substrate is prothrombin. Xa also somehow got assigned the term “thrombokinase,” coined by Morawitz in the 1920s who postulated four related coagulation factors, a seminal event in coagulation understanding. For simplicity, we’ve almost universally dropped the descriptive names (also eponyms like Stuart-Prower) in favor of the Roman numerals these days. Though your student is technically correct to use “thrombokinase” for factor Xa, I would encourage her to use “Xa,” just so people like me know what she is talking about. I wish her success on her project.