Regulation of Rabbit Liver Fructose-1, 6-diphosphatase

Abstract

In the modification of rabbit liver D-fructose-1,6-diphosphate 1-phosphohydrolyase [fructose-1,6-diphosphatase, EC 3.1.3.11], cathepsin B₁ [EC 3.4.4.−] from the lysosomal particles was considered to play an important role. The modifying reaction required a sulfhydryl compound and was inhibited by N-α-p-tosyl-L-lysine chloro-methyl ketone (TLCK) and L-l-tosylamide-2-phenylethyl chloromethyl ketone (TPCK). The optimum pH for the modification reaction was 5.0. The affinity of the modifying enzyme for fructose-1,6-diphosphatase was very high with an apparent Km of 5×10⁻³M. The modified fructose-1,6-diphosphatase showed an alkaline pH optimum, and the activity at pH 8.6 was increased by approximately four-fold, whereas the untreated enzyme showed a neutral pH optimum. The modification was considered to be a result of partial proteolysis of fructose-1,6-diphosphatase subunits by the modifying enzyme.