Biochemistry. — "Further Researches on the Antagonism betioeen 

 Citrate and Calcium Salt in Biochemical Processes, Examined 

 by the Aid of Substituted Citrates". (First Communication). 

 By Dr. J. R. Katz. (Communicated by Prof. A. F. Holleman). 



(Communicated at the meeting of May 26, 1923). 

 I. Exposition oj the Problem. ' 



In an earlier research ') I have tried to analyse the natnre of 

 (lie biological citrate action. After addition of citrate a biological 

 liquid behaves as if it no longer contains any fi'ee. calcium ions; 

 addition of citrate acts, therefore, in the same way as addition of 

 oxalate or fluoride. With this difference, however, that the action 

 of the latter salts rests on the formation of a very little soluble 

 precipitate, and that a gypsum solution remains perfectly clear after 

 addition of citrate. Complex ions must, therefore, have been formed'); 

 it is only the question, how they are constituted. 



In order to bring light in this still dark question, I compared at 

 the time the action of the citrates with that of substituted citrates, 

 in which one or more of the groups which possibly can bind the 

 Ca to complexes (the alcohol group and the three carboxyl groups) 

 were made inactive by substitutions (acetylation of the alcohol group; 

 the carboxyl group esterified or converted to acid amide etc.). As 

 typical representative of a biological citrate action the inhibition of 

 the rennet coagulation of milk was investigated. 



It then appeared that when either the alcohol group or one of 

 the carboxyl groups is made inactive, the citrate action in a V,, 

 N. solution is reduced to V,, of its strength; (i.e. is made equally 

 weak as in a citrate solution of '/n of the same strength), the 

 removal of two or more groups reducing the action to less than 

 '/loo of the original value. When the alcohol group is made inactive, 

 the action appears to be equally sti'ong as in other tri-or tetra-basic 

 acids of allied structure, but without oxy-group (as tri-carballyllic 

 acid, aconitic acid or iso-allylene tetra-caibonic acid. When one 



1) These Proc. Vol. XV, p. 434. 



») Sabatani, Atti della R. Acad, di Torino 36, p. 27—53 and Memoiie (2) 52, 

 p. 213—257 was the first to adduce arguments for this theory. 

 Bromberg, Diss. Amsterdam. 



