Unlike Apache 1.3, Apache 2 requires more than one module for mod_proxy functionality. Apache 1.3 requires only mod_proxy for basic proxy support. Apache 2 requires mod_proxy in addition to protocol-specific modules depending on the type of proxying required:

LoadModule proxy_module            /path/to/mod_proxy.so
LoadModule proxy_http_module       /path/to/mod_proxy_http.so

ProxyRequests off

<Proxy *>
   Order deny,allow
   Allow from all
</Proxy>

<VirtualHost *:80>
   ServerName localhost
   UseCanonicalName Off
   ProxyPass /other/ http://otherserver:8888/
   <Location /other/>
      ProxyPassReverse /
   </Location>
</VirtualHost>