Skeletal muscle calcium channel ryanodine binding activity in genetically unimproved and commercial turkey populations

The biochemical basis for the incidence of pale, soft, exudative (PSE) turk ey meat was investigated by conducting ryanodine binding experiments on sar coplasmic reticulum (SR) vesicles prepared from genetically unimproved and commercial turkeys. Ryanodine binding to the Ca2+ channel protein in SR ves icles from both populations of turkeys was activated at a threshold concent ration of approximately 0.2 mu M Ca2+, reached a plateau over the range of 3 to 30 mu M free Ca2+, and was only slightly inhibited at 1 mM Ca2+. The S R fractions, enriched in the Ca2+-channel protein, from commercial turkeys exhibited a higher (P < 0.05) mean affinity for ryanodine when compared to that from unimproved turkeys (K-d = 12.2 vs 20.5 nM, respectively). A fourf old difference (P < 0.05) in mean Ca2+-channel protein content or B-max (1. 10 pmol/mg vs 4.01 pmol/mg) was observed between commercial and unimproved turkey SR fractions. The apparent difference in channel protein content bet ween the two populations may be partially accounted for by the high abundan ce of a 75-kDa protein, as yet unidentified, observed in most commercial tu rkey samples on SDS polyacrylamide gels. The differences in ryanodine bindi ng activity between these two populations of turkeys suggest that altered S R calcium channel protein activity, or altered channel regulation, may be a ssociated with the increased incidence of PSE meat from turkeys selected fo r growth characteristics.