EVIDENCE FOR PROTEIN DAMAGE AT ENVIRONMENTAL TEMPERATURES - SEASONAL-CHANGES IN LEVELS OF UBIQUITIN CONJUGATES AND HSP70 IN THE INTERTIDAL MUSSEL MYTILUS-TROSSULUS

We examined the seasonal variation in environmentally induced protein damage in natural populations of the intertidal mussel Mytilus trossul us, In order to compare the state of protein pools during seasonal var iations in environmental temperature, we,used solid-phase immunochemic al analysis to quantify ubiquitin conjugate concentrations and relativ e levels of the stress protein hsp70, The two biochemical indices were selected far their cellular roles in irreversible and reversible prot ein denaturation, respectively, Proteins that are ubiquitinated are ir reversibly damaged and are degraded by intracellular proteases; stress proteins act as molecular chaperones to re-fold thermally denatured p roteins and, thus, indicate degrees of reversible protein damage, Comp arisons involved mussels collected in February and August from two stu dy sites: an intertidal site which subjected animals to a wide range o f body temperatures (from approximately 10 to 35 degrees C in summer), and a subtidal site where animals remained submerged throughout the t idal cycle, Our results show that quantities of ubiquitin conjugates a nd hsp70 were greater in gill tissue from summer-collected mussels tha n in gills of winter-collected specimens, Ubiquitin conjugate and hsp7 0 levels were also greater in mussels collected from an intertidal loc ation than in mussels from a submerged population, Our results show th at the high summer temperatures normally experienced in the field are sufficient to cause increased denaturation of cellular proteins. Despi te increases in the concentrations of heat shock proteins in summer-ac climatized mussels, elevated levels of irreversibly denatured, i.e, ub iquitinated, proteins were still observed, which indicates that the he at shock response may not be able to rescue all heat-damaged proteins, The energy costs associated with replacing heat-damaged proteins and with maintaining the concentrations and activities of heat shock prote ins may contribute substantially to cellular energy demands, These inc reased energy demands may have an impact on the ecological energetic r elationships of species, e,g, in the allocations of energy for growth and reproduction, and, as a consequence, may contribute to determining their distribution limits,