Fructose-1,6-bisphosphate affects the rate of a large variety of enzyme reactions. In some instances its role as a physiologic effector is well documented. In many cases the effects of fructose bishosphate on particular enzymes have been demonstrated in vitro but the link to physiologic conditions has not yet been established. It is the purpose of this paper to summarize the scattered findings in fructose bisphosphate as an effector of enzyme reactions and to draw some conclusions about the role of the compound in metabolic regulation.

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A PROTEOLYTIC ENZYME FROM RABBIT SPLEEN 543 amount of products which are not precipitable by trichloroacetic acid. 2. The enzyme responsible for this proteolytic activity has been purified by adsorption of inactive material on diethylaminoethylcellulose and carboxymethylcellulose. 3. Chromatography on diethylaminoethylcellulose has demonstrated the existence of only one enzyme in the purified preparation. 4. The optimum pH and the Michaelis constant of this enzyme are the same as those of the proteolytic activity in the crude preparation. It was therefore concluded that this enzyme is responsible for the proteolytic activity of the crude spleen extracts. 5. A comparative study of the immunoelectrophoresis patterns given by human-serum albumin, degraded with the crude and purified spleen extracts, has shown that it is this enzyme which is responsible in both cases for the splitting of the antigenic structure of human-serum albumin. We wish to thank Dr P. Grabar for his advice and Mrs J. Cavillon for her technical assistance. One of us (C.L.) aoknowledges the support of the Institut National d'Hygiene, Paris. This work was done while T.W. was a post-doctoral research fellow of the Life Insurance Medical Rewearch Fund.