Purified GAI, one form of glucoamylase obtained from Aspergillus niger mutant T21 contained 17.6% total carbohydrate. Analyses of amino acid composition showed that GAI contained about 25% Ser and Thr, 20.3% Asx and Glx and 6% basic amino acids. The UV absorption and fluorescence spectra of GAI were determined. The maximum absorption wavelength was at 278nm and minimum at 250nm. For fluorescent analyses the excitation and maximum emission spectra were at 284nm and 342nm respectively. The CD-spectrum determined showed two negative peaks. Its dispersion of secondary structure in solution showed 10.6% ?-helix, 16.3% ?-form and 73.1% unordered.

HK-2 cells cultured in vitro were divided into three groups: normal glucose group ( NG ), high glucose group( HG), and mannitol group(MG). The expression of angiotensin-converting enzyme( ACE ) and ACE2 mRNA in HK-2 cells was detected. The concentration of angiotensin Ⅱ ( Ang Ⅱ ) in the culture medium was detected. The mRNA and protein expression of ACE and ACE2 existed in normal cultured HK-2 ( NG group ). In comparison with NG group, the mRNA and protein expressions of ACE in HG group increased significantly ( P＜0. 01 ), and the expression of ACE2 mRNA decreased significantly( P＜0. 01 ). The level of Ang Ⅱ in HG group was significantly higher than in NG group( P＜0. 05 ). The result show that high glucose may induce ACE expression and inhibit ACE2 expression, then promote synthesis of Ang Ⅱ in proximal tubular cells.