apc most likely going to rapidly crash and high cpu load with php53u (based on personal experiences).
But i you insist to use APC, you can install it with pecl.
Just type
pecl install apc
and then you can adjust your apc setting in /etc/php.d/apc.ini
p/s:
you can also install ZendOPCache with pecl install zendopcache-7.0.2 (latest version)... It's works better than apc (in my opinion)