Thermostabilization of ovalbumin in a developing egg by an alkalinity-regulated, two-step process

Native ovalbumin has been known to convert into a heat-stable form, S-ovalb umin, either in an avian shell egg or in an isolated ovalbumin solution. Re cently, similar conversion of ovalbumin in fertile eggs was also reported. We found that the conversion into S-ovalbumin was slower in fertile eggs th an in unfertile eggs under the same incubation conditions on the basis of c alorimetric analyses for the samples isolated from those eggs. During the i ncubation, there were differential pH changes of white in the fertile and u nfertile eggs. When the pH of purified ovalbumin was manually adjusted so a s to simulate the pH changes of egg white during the incubation, the course of the conversion into S-ovalbumin was very similar to that either in fert ile or unfertile eggs. Therefore, we conclude that thermostabilization of o valbumin in fertile eggs proceeds by a certain mechanism which depends on t he alkalinity of egg white.