434 
Biochemistry. — “The antagonism between citrates and caleiumsalts 
in milkcurdling by rennet. A contribution to the knowledge 
of the relation between structure and biological action”. | First 
communication’. By J. R. Katz. (Communicated by Prof. 
A. F. HorLEMAN). 
(Communicated in the meeting of April 26, 1912). 
Introduction. 
A small quantity of neutral citrates prevents the coagulation of 
blood; various salts which precipitate calcium as an insoluble com- 
pound, e.g. oxalates and fluorides, have an analogous action. The 
peculiarity of the case is however that citrates do not precipitate 
diluted solutions of calciumsalts, but remain entirely clear; notwith- 
standing this, they have neutralized the effect of the calcium. 
A similar antagonism between citrates and calcium has been found 
in various biochemical and pharmacological processes. 
Citrates in small quantity prevent the curdling of milk by rennet; 
various immunochemical reactions are prevented by citrates, as the 
laking of red bloodcorpuscles by animal hemolysines (eelserum 
cobralecithide, normal complement); here also the action of citrates 
is prevented by the addition of calciumsalt*). 
Recently Prof. HAMBURGRR has shown that the phagocytic power 
of the leucocytes is inhibited by citrates and is reactivated by calcium- 
salts and that fluorides and oxalates too prevent phagocytosis. 
The pharmacological action of citrates shows the same antagonism 
with ecaleiumsalts, e.g. JANUsHKH?) has found that the paralysis of the 
heart and the paralysis of the nervous system caused by intravenous 
injection of citrates, is removed by injection of calcium. Busq and 
PacHon *) showed, that there exists antagonism between the action 
of citrates and calcium on the heartmuscle, and Mac CALLUM *) 
observed that the purgative action of citrates is inhibited by addition 
of calciumsalt. 
It seems perfectly clear, that substances as fluorides and oxalates 
which precipitate calcium as a nearly insoluble compound, are anta- 
gonists of calcium, but how shall we explain, that citrates have the 
same action, although they do not precipitate calciumsalt? 
As this property of citrates is used more and more in hema- 
1) Genaou, Arch. Intern. de Physiologie 7 (1903). 
2) Arch. f. Exper. Pathol. u. Pharmak. 61. p. 363—375. 
5) C.R. 148 p. 575—578. 
*) Americ, Journ. of Physiol. 10, p. 101—110. 
