code: public function listMarketplaceParticipations($request)
      {
          if (!($request instanceof MarketplaceWebServiceSellers_Model_ListMarketplaceParticipationsRequest)) {
              $request = new MarketplaceWebServiceSellers_Model_ListMarketplaceParticipationsRequest($request);
          }
          $parameters = $request->toQueryParameterArray();
          $parameters['Action'] = 'ListMarketplaceParticipations';
          $httpResponse = $this->_invoke($parameters);
  
          $response = MarketplaceWebServiceSellers_Model_ListMarketplaceParticipationsResponse::fromXML($httpResponse['ResponseBody']);
          $response->setResponseHeaderMetadata($httpResponse['ResponseHeaderMetadata']);
          return $response;
      }
docs: List Marketplace Participations
  Returns a list of marketplaces that the seller submitting the request can sell in,
  and a list of participations that include seller-specific information in that marketplace.
  
  @param mixed $request array of parameters for MarketplaceWebServiceSellers_Model_ListMarketplaceParticipations request or MarketplaceWebServiceSellers_Model_ListMarketplaceParticipations object itself
  @see MarketplaceWebServiceSellers_Model_ListMarketplaceParticipationsRequest
  @return MarketplaceWebServiceSellers_Model_ListMarketplaceParticipationsResponse
  
  @throws MarketplaceWebServiceSellers_Exception