How to enable a disabled Tab

[gikotim]

Hi!
I have a MenuTabs with one tab initially disabled. When a button is clicked I want to enable this menu-Tab.
I see the property but I don't know how to access/change it:

SPA.menuTabs.get(0).properties.items[3].disabled = "false";
doesn't work.
Can you help me, please?

[linb]

SPA.menuTabs.updateItem('the id', {disabled :false});