$(document).ready(function () 
{ 
        $('#street').autocomplete({
    serviceUrl: '/classes/json.php',
    minChars: 2,
    deferRequestBy: 300,
    params: { 'reg': $('#sregion').val()},
    onSelect: function (suggestion) { 
    alert($('#sregion').val());
      $('#street').val(suggestion.value);   
    }
});
});

function reenable(){
         var ac =       $('#street').autocomplete({
    serviceUrl: '/classes/json.php',
    minChars: 2,
    deferRequestBy: 300,
    params: { 'reg': $('#sregion').val()},
    onSelect: function (suggestion) { 
      $('#street').val(suggestion.value);   
    }
    
    
        
});
        }

ac.disable();
ac.enable();
ac.setOptons({  params: { 'reg': $('#sregion').val()} });