emacs-app does not find latex

[Andre Massing]

Hey!

For some reasons, emacs-app does not find my latex installation (Mactex, 
bin files are located in /usr/texbin).
I installed emacs-app together with the auctex package (using +emacs_app 
+mactex variants)
When I run pdflatex via the command menu, I only got the message

Running `Preview-LaTeX' on `paper' with ``pdflatex  
"\nonstopmode\nofiles\PassOptionsToPackage{active,tightpage,auctex}{preview}\AtBeginDocument{\ifx\ifPreview\undefined\RequirePackage[displaymath,floats,graphics,textmath,sections,footnotes]{preview}[2004/11/05]\fi}" 
"\input" paper.tex''
/bin/sh: pdflatex: command not found

Preview-LaTeX exited as expected with code 127 at Mon Nov  8 13:58:07
LaTeX: LaTeX found no preview images

indicating that pdflatex was not found. But the /usr/texbin is added to 
my PATH variable and I added it as well to the exec-path of emacs.
Do you have any idea about what goes wrong or where I could start to 
investigate. I am fairly new to emacs so I don't know anything about
the internals of auctex...

My minimalistic .emacs file is
(require 'tex-site)
(load "auctex.el" nil t t)
(load "preview-latex.el" nil t t)
(add-to-list 'load-path "~/.emacs.d/site-lisp/")
(setq exec-path (append exec-path '("/usr/texbin/")))


Any help or hints are really appreciated!

Best regards,
Andre