Reduced enzyme activity following Hsp70 overexpression in Drosophila melanogaster

Acclimation to environmental change can impose costs to organisms. One pote ntial cost is the change in cell metabolism that follows a physiological re sponse, e.g., high expression of heat shock proteins may alter specific act ivity of important enzymes. We examined the significance of this cost in a pair of Drosophila melanogaster lines transformed with additional copies of a gene that encodes the heat shock protein, Hsp70. Heat shock induces Hsp7 0 expression in all lines, but lines with extra copies produce much more Hs p70 than do excision control strains. The consequence of this supranormal H sp70 expression is to reduce specific activity of both enzymes analyzed, ad ult alcohol dehydrogenase (ADH), which is heat sensitive, and lactate dehyd rogenase, which is not. Strain differences were most pronounced under those conditions where Hsp70 expression was maximized, and not where the heat st ress denatured proteins. That result supported the idea that peptides when overabundant within the cell.