440 2. ANALOGS OF ENZYME REACTION COMPONENTS 



phosphatases about as potently as phosphate and probably combine with 

 the enzymes in a similar manner. Certain carboxylates (oxalate, malonate, 

 malate, citrate, glucarate, gluconate, lactate, and others) have been found 

 to be inhibitory, but most of these are not remarkably effective, probably 

 binding to enzyme cationic groups to various degrees or chelating with 

 metal ions. However, ( + )-tartrate* is a very potent inhibitor of certain 

 phosphatases, as first shown by Abul-Fadl and King (1949) and confirmed 

 by Anagnostopoulos (1953), and is so much more active than other anions 

 that the mechanism has been investigated in several excellent studies. 



The phylogenetic relationships of ( + )-tartrate inhibition and the vari- 

 able susceptibilities of phosphatases from different tissues are quite inter- 

 esting. Abul-Fadl and King (1949) found that although prostatic acid phos- 

 phatase is very sensitive, no effects are exerted on the acid phosphatases of 

 erythrocytes or plasma, and Anagnostopoulos (1953) noted no inhibition 

 with the phosphatases of mustard, wheat germ, or Aspergillus. Kilsheimer 

 and Axelrod (1958) investigated the effects of ( + )-tartrate on the phospha- 

 tases from many sources and found that at 20 mM the inhibitions vary 

 from to 93%. They concluded that animal phosphatases are more suscep- 

 tible than plant phosphatases, and that bacterial phosphatases are generally 

 resistant. It was suggested that ( + )-tartrate may be of taxonomic use in 

 those more primitive organisms where it is difficult to decide whether they 

 are plants or animals. 



The earliest work demonstrated that the inhibition is stereospecific, nei- 

 ther ( — )-tartrate nor meso-tartrate exerting appreciable effects on prostatic 

 phosphatase, and this has been confirmed in all the recent studies. In the 

 series of phosphatases tested by Kilsheimer and Axelrod (1958) it was ob- 

 served that very few of the enzymes are affected by (— )-tartrate and 

 these are inhibited only slightly. The iiT/s were determined by London et 

 at. (1958) as 0.13 mM for ( + )-tartrate and 93 mlf for (-)-tartrate on 

 prostatic acid phosphatase. It is strange that they found meso-tartrate to 

 be an effective inhibitor {K^ = 0.4 mM) in contrast to all other work. 

 The acid phosphatase from Neurospora crassa is inhibited completely by 

 12 mM ( + )-tartrate but is unaffected by 50 mM ( — )-tartrate or meso- 

 tartrate (Kuo and Blumenthal, 1961). In all cases the inhibition by ( + )- 

 tartrate is competitive with respect to substrate. The inhibition is thus more 

 marked with /^-glycerophosphate as the substrate than with phenyl phos- 

 phate or p-nitrophenyl phosphate, since the former substrate is bound less 

 tightly (Nigam at al, 1959; Kuo and Blumenthal, 1961). 



Tartrate and related inhibitors have been used to map the active site 

 of prostatic phosphatase (London et al., 1958). The K/s and estimated 



* There has been confusion in the nomenclature of the tartrates and the dextro- 

 rotatory ( + )-tartrate has been designated as l- or D-, depending on the system used. 

 To avoid ambiguity I shall indicate the isomers by the signs of their rotation. 



