Homocysteine increases the stable association between GRP78 and vWF. HUVEC cultured in the absence or presence of 0.2, 1.0, or 5.0 mmol/L homocysteine for 8 or 18 hours were metabolically labeled for 1 hour in the presence of [³⁵S]methionine and [³⁵S]cysteine. Radiolabeled proteins from cell lysates were immunoprecipitated with anti-vWF antibodies, separated on 7.5% SDS polyacrylamide gel under reducing conditions, and detected by fluorography. Immunoprecipitation of pro and mature vWF coprecipitated GRP78. kD, molecular mass markers.