MATLAB: How should I write a value such as “0.9 micromolar^-1.sec^-1” in the code

input

Okay, so my question is if I have a value such as 0.9 micromolar^-1.sec^-1. How should I enter this value in the code.
Which of these is the correct one?
v = 0.9e-6
or
v = 0.9e6

v = 0.9
 v = 0.9 / 1e-6