private function _convertListSubscriptions($request) {

        $parameters = array();
        $parameters['Action'] = 'ListSubscriptions';
        if ($request->isSetSellerId()) {
            $parameters['SellerId'] =  $request->getSellerId();
        }
        if ($request->isSetMWSAuthToken()) {
            $parameters['MWSAuthToken'] =  $request->getMWSAuthToken();
        }
        if ($request->isSetMarketplaceId()) {
            $parameters['MarketplaceId'] =  $request->getMarketplaceId();
        }

        return $parameters;
    }