Yes, you can usually spray acrylics over enamels without problems - heck, I spray Future over my laquer color coats all the time, and it's an acrylic - but, as with anything, you want to test it first. Laquer over enamels is also fine.
I added the caution because most paint manufacturers use the rule of thumb of "acrylics over acrylics, enamels over acrylics or enamels, and laquers over acrylics, enamels or laquers" (see Testors home page for more info). An acrylic over enamel or laquer may not always cure properly. The best bet for success is to let the enamel or laquer cure thoroughly before spraying acrylic over it. Never apply acrylics over wet or damp enamel or laquer.
Glenn