EFFECT OF DEFICIENCY IN ANIMALS 



Avidin 



The first attempt to isolate the factor in egg white responsible for 

 producing biotin deficiency in rats and chicks was made by R. E. 

 Eakin, E. E. Snell and R. J. Williams, ^^ who showed that biotin was 

 inactivated by egg white in vitro and that it was immaterial how 

 crude the biotin preparation was. Purification of the egg-white 

 factor, for which the name avidin was suggested,^^ was effected by 

 precipitation with acetone and five-sixths saturation of the aqueous 

 solution with ammoniam sulphate. The biotin was not released from 

 the complex by dialysis, but could be recovered after the complex 

 had been steam-sterilised. This was consistent with the observation 

 that cooked egg white did not inactivate biotin. Avidin was eventu- 

 ally obtained in crystalline form,^^ when it was shown to have the 

 properties of a protein with a large carbohydrate moiety. A similar 

 substance was isolated by D. W. Woolley and L. G. Longsworth i^^ 

 it had an isoelectric point at pH lo and was homogeneous in electro- 

 phoresis and sedimentation experiments. 



The discovery of the inactivation of biotin by avidin is of obvious 

 importance in nutrition. P. Gyorgy and C. S. Rose ^^ showed that 

 whole egg contained an excess of avidin, the biotin in the yolk being 

 unable to neutralise all the avidin in the white. Thus in order to 

 utilise the biotin in eggs, these must be cooked in order to destroy 

 the avidin. A case of biotin deficiency resulting from a diet consisting 

 exclusively of raw eggs has been described. ^'^ 



P. Gyorgy and C. S. Rose ^^ also showed that biotin was present in 

 egg yolk in a non-dialysable form of high molecular weight, which 

 stimulated the growth of yeast and of rats made biotin-deficient by 

 means of egg white. Biotin was not released from the biotin-avidin 

 complex by incubation with pepsin, trypsin, pancreatin, papain or 

 with liver, muscle or blood, but was liberated by oxidation with 

 0-45 % hydrogen peroxide at pB. 3. Avidin was destroyed by light, 

 especially in presence of riboflavine, and biotin could be liberated 

 from the complex by irradiation. ^^ 



A form of biotin that will not combine with avidin has been stated 

 to exist in normal rat urine, human urine and urine from rats fed egg 

 white, but not in any other biological materials (see page 433).^*^ 



K. Meyer ^^ and W. L. Laurence ^^ suggested that, since biotin 

 increased the lytic action of lysozyme and avidin, the biotin-avidin 

 complex might be identical with lysozyme, the factor that brings 

 about lysis of bacteria. Alderton et al.,^^ however, failed to confirm 

 the stimulatory effect of biotin on the lytic action of purified crystalline 

 lysozyme, which was in fact shown to contain only traces of biotin. 

 Moreover, lysis by avidin preparations was not increased by biotin, 

 and avidin did not inhibit the lytic action of lysozyme. 



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