Hi Scott,
Welcome to RootsChat !
there is a german place name site here: 
http://gov.genealogy.net/index.jspwhich allows you to enter "Word beginning with ..."
Altans and Mackbuck weren't there, but
altan... gives
Altanmut   Ostpreußen 
and Mack... gives 
Mäckelsdorf 37284, W3441 Hessen RB Kassel - Werra-Meißner-Kiels   
Macken 56290, W5449 Rheinland-Pfalz RB Koblenz - Mayen-Koblenz   
Mackenbach, Lohmar 53797, W5201 Nordrhein-Westfalen RB Köln - Rhein-Sieg-Kreis JO30PU 
Mackenbach, Kr Kaiserslautern 67686, W6751 Rheinland-Pfalz RB Rheinhessen-Pfalz - Kaiserslautern JN39SL 
Mackenbrede, Leopoldshöhe   Nordrhein-Westfalen - - JO41IX 
Mackenbruch, Oerlinghausen   Nordrhein-Westfalen - - JO41IX 
Mackendorf 38459, W3331 Niedersachsen RB Braunschweig - Helmsfedt JO52MI 
Mackenheim 69518 Hessen - - JN49JN 
Mackenheim 67390   JN38SE 
Mackenmühle 91785, W8835 Bayern RB Mittelfranken - Weißenburg-Gunzenhausen 
Mackenbach or Mackenbruch are possibilities (swallow the 'en' !)
I don't know if any of that means anything to you (geographically) so a question for you:  has anybody ever said anything about which area of Germany, )North, South, Bavaria, etc) he came from  ??
Another thought:  Mackbuck could be Magdeburg, the G is pronounced so hard that it could be heard as a K
Any info. you have, share it with us !! (please !)
Further avenues to explore:  
- did they become naturalised 
- did they have to register as aliens (WW1 ) 
(see the threads on this board on this subject)
Good luck,
Bob