The easiest way of doing (I think) what you're asking is to use PyMEL as it has a really convenient interface for this including the ability to pass the expected function parameters. First import PyMEL as follows:
Then use PyMEL's "mel" object to execute the MEL command as follows:
pm.mel.sphere(r=100)
Maya's MEL commands are already provided in PyMEL but if you're trying to execute a function written by others (a third party or even yourself) just follow the syntax:
pm.mel.your_command(params_if_any)
For more info run: help(pm.mel)
Hope that helps!