Now look at the Lineweaver-Burke plot of 1/Vo vs. 1/[substrate], aka the double reciprocal plot. The important things to remember about Lineweaver-Burke plots are the x and y intercepts. The x-intercept = -1/Km, and the y-intercept = 1/Vmax. Just learn these, and I'll help you make sense of them by discussing inhibition."Vmax is the maxim intial velocity (Vo) that an enzyme can achieve. Initial velocity is defined as the catalytic rate when substrate concentration is high, enough to saturate the enzyme, and the product concentration is low enough to neglect the rate of the reverse reaction. Therefore, the Vmax is the maximum catalytic rate that can be achieved by a particular enzyme.
Km is determined as the substrate concentration at which 1/2 Vmax is achieved. This kinetic parameter therefore importantly defines the affinity of the substrate for the enzyme." From answer.com
Hence higher the Km lower the affinity such as with Glucokinase and reverse with Hexokinase.