Enzymatic properties of the N- and C-terminal halves of human hexokinase II

Although previous studies on hexokinase (HK) II indicate both the N- and C-terminal halves are catalytically active, we show in this study the N-terminal half is significantly more catalytic than the C-terminal half in addition to having a significantly higher K-m for ATP and Glu. Furthermore, truncated forms of intact HK II lacking its first N-terminal 18 amino acids (Delta 18) and a truncated N-terminal half lacking its first 18 amino acids (Delta 18N) have higher catalytic activity than other mutants tested. Similar results were obtained by PET-scan analysis using F-18-FDG. Our results collectively suggest that each domain of HK II possesses enzyme activity, unlike HK I, with the N-terminal half showing higher enzyme activity than the C-terminal half. [BMB reports 2009; 42(6): 350-355]