Extjs calling function from object declaration

Question

I have this code:

Ext.define('DKM.BaseClasses.Stores.BaseStore', {
requires:['Ext.window.MessageBox'],
extend: 'Ext.data.Store',

proxy:  {
        type:'ajax',
        listeners: {
            exception: function(proxy, response, options) {                 
                requestMessageProcessor(proxy, response);
            }

        },
        afterRequest: function(request, success) {

            requestMessageProcessor(request.scope, request.operation.response);
        },
},      

requestMessageProcessor: function(proxy, response) {
...

What I would like to do is to call requestMessageProcessor. The problem (maybe a scope problem) is that I recieve an error "requestMessageProcessor is not a function".

Can anybody give me an advice?

Thanks in advance! David