The Role of Myokinase in Transphosphorylations* I. the Enzymatic Phosphorylation of Hexoses by Adenyl

The enzyme which catalyzes the phosphorylation of glucose and fructose was described in 1927 by Meyerhof (1). He found that muscle extracts which split polysaccharides and hexose phosphates to lactic acid but were unable to ferment hexoses could be enabled to ferment glucose and fructose by addition of a protein fraction from bakers’ yeast. The same protein fraction activated the aerobic oxidation of hexoses in the hemolysate from red cells (2). The yeast protein was named hexokinase to indicate that it initiates the metabolism of hexoses. The nature of the hexokinase reaction was revealed by studies of von Euler and Adler (3) and of Meyerhof (4) in 1935. Van Euler and Adler observed that the crude hexose monophosphate dehydrogenase (Zwischenferment) obtained from yeast by Warburg and Christian in 1933 (5) was able to oxidize not only hexose monophosphate but also unphosphorylated glucose and fructose, provided that adenosine triphosphate was added to the system. Van Euler and Adler showed that the action of adenosine triphosphate was due to an enzymatic transfer of the labile phosphate groups of this nucleotide to glucose or fructose, thus forming hexose monophosphate, the substrate to be oxidized. The yeast enzyme cahalyzing this phosphate transfer was called heterophosphatese. Meyerhof (4) subsequently showed that the hexokinase, too, catalyzes a transfer of phosphate from adenosine triphosphate to glucose. This explains the action of hexokinase on the fermentation of monohexoses in muscle extracts, since small amounts of adenyl pyrophosphate are formed continuously as soon as the fermentation is started and the limiting factor