90-kDa heat shock protein (hsp90) was purified from the mammary tissue of a Holstein cow in late lactation. Contents of the hsp90 in mammary tissues from Holstein heifers and cows in lactating and involuting periods were measured by quantitative immunoblotting, using rabbit antiserum raised against purified hsp90. The contents of hsp90 were higher in tissues from lactating cows than in those from heifers and involuting cows. The elevated concentrations of mammary hsp90 in lactation suggest that this protein is involved in lactation.
(Lab. of Clinical Biochemistry, Hokkaido Research Station)
