The sample was centrifuged at 500g for 20 min (Heraeaus Multifuge, Osterode, Germany) and an aliquot of 4 ml was
transferred to Eppenderf vials and frozen to 18 C for 30 min or more and subsequently microcentrifugated at 12,100g for 10 min (Eppendorf Ag Minispin Centrifuge, Germany).