508 J. BRACKET 



might be selected and arranged in a polypeptide chain, it seems impossible 

 to explain, on that basis alone, the synthesis of specific proteins (Chan- 

 trenne^^^) . 



It has been pointed out by Reiss,^^- as well as by Bergmann and 

 Fruton,^^^ that protein synthesis under the action of proteolytic enzymes 

 would be favored if the reaction products were elircijiated : this might 

 occur in a polyphasic system, such as the cell, where adsorption or incor- 

 poration of the synthesized products on cytoplasmic particles (microsomes, 

 for instance) could drive the reaction towards synthesis. Careful study 

 of proteases distribution in the various cell particles would be necessary 

 before such a possibility could be put to a test. 



There are only a few indications that proteases might play a synthetic 

 role in the cell: for instance, Schultz^^' found that fasting decreases simul- 

 taneously the number of cell particles in the liver and the amount of ca- 

 thepsin II: this enzyme is apparently bound to cytoplasmic granules and it 

 might play a role in protein synthesis. A similar relationship between 

 catheptic activity and fixation of amino acids has been pointed out by 

 Rothschild and Junqueira,^^^ while Kritsman et al}'^^ report that incorpora- 

 tion of labeled amino acids into serum proteins is increased by the addition 

 of proteolytic enzymes. While the evidence for an intervention of protease^ 

 in protein synthesis and amino acid uptake by proteins is rather meager, 

 it is by no means nonexistent, and further work in that direction is ob- 

 viously needed before any conclusions can be drawn. 



A much better understanding of the role of PNA in protein synthesis 

 would be reached if a recent preliminary report by Binkley^^* could be 

 confirmed that a dipeptidase, cysteinylglycinase, is of a pentose-polynucleo- 

 tide nature. According to Binkley, the enzyme responsible for the hydroly- 

 sis of cysteinylglycine in pig kidney is identical with PNA. 



The facts that this preparation is stable towards proteolytic enzymes 

 and that it shows a typical nucleic acid absorption spectrum provide 

 evidence for its PNA nature; however, as pointed out by Binkley^^® him- 

 self, the finding that the enzyme also resists ribonuclease digestion "is a 

 source of some concern." Chantrenne's^^^ observation that there is no 

 parallelism between the sedimentation of cysteinylglycinase and of PNA 

 when pigeon liver homogenates are centrifuged is a further reason for 

 doubting the validity of Binkley's preliminary conclusions. 



'^- P. Reiss, "L'action du potentiel d'oxydo-r^duction du milieu sur I'activit^ des 

 proteinases: hydrolyse et condensation." Clermont-Ferrand. 1942. 



'53 J. Schultz, J. Biol. Chern. 178, 451 (1949). 



1'^ H. A. Rothschild and L. C. U. Junqueira, Arch. Biochern. and Biophys. 34, 453 

 (1951). 



'96 M. G. Kritsman, A. S. Konikova, and T. D. Osipenko, Biokhimiya 17, 488 (1952). 



'98 F. Binkley, Exptl. Cell Research Suppl. 2, 145 (1952). 



1" H. Chantrenne, Arch, intern, physiol. 60, 186 (1952). 



