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651.
Further studies on the mechanism of phenol-sulfuric acid reaction with furaldehyde derivatives 总被引:1,自引:0,他引:1
Even though the chromogens formed from mannose and galactose showed comparable absorbances at 480 nm in the conventional (developer present during heat of dilution) and modified (developer reacted at room temperature after cooling; epsilon mannose = 13,700, galactose = 14,000) phenol-sulfuric acid reactions, shoulders in the region 420-430 nm were prominent in the former method. Fucose was 10 times less reactive in the modified method (epsilon = 800) than in the conventional method. 2-Formyl-5-furan sulfonic acid reacted equally efficiently in the two methods (epsilon = 40,800). 5-Methyl-2-furaldehyde, unlike the sulfonate derivative or 5-hydroxymethyl-2-furaldehyde, required heat for condensation with phenol. 2-Furaldehyde dimethylhydrazone reacted 25 times better to form a chromogen (epsilon = 40,500) in the modified phenol-sulfuric acid method. The possible roles of intermediates between hexoses and furaldehydes in forming chromogens and the effect of substitution at the 2- and 5-positions of furaldehyde on the rates of condensation with phenol for the observed differences between the conventional and the modified methods are discussed. 相似文献
652.
Normal human blood plasma showed hydrolytic activities on several synthetic substrates for proteases, the most effective being
H-D-Ile-Pro-Arg-p-nitroanilide, H-D-Pro-Phe-Arg-p-nitroanilide and H-D-Val-Leu-Arg-p-nitroanilide. When plasma was preincubated
for 12 h at 37°C, there was no significant alteration of the hydrolytic activities. On incubation for 12 h with king cobra
venom (2 μg for 0.1 ml plasma), there was considerable decrease in the activities and complete abolition of the protease binding
capacity of α2-macroglobulin. On chromatography on Sephadex G-200, α2-macroglobulin activity and bulk of the protease activity of normal plasma were eluted in the void volume region. A minor
protease peak was eluted with aVe/Vo value of 2.5. With venom treated plasma, there was no decrease with this peak. The major protease peak and α2-macroglobulin activity were drastically reduced. Chromatography on red Sepharose showed that all the α
2
−
acroglobulin activity and bulk of the protease activity in normal plasma were bound to the column. In venom treated plasma
there was marked reduction in the bound fraction. The data suggest that cobra venom proteases directly or through proteases
generated in plasmain situ causes limited cleavage of α2-macroglobulin as well as α2-macroglobulin bound proteases, inactivating them. 相似文献