Transconformation of casein was studied by using the technique of ultraviolet absorption spectra and its difference spectra in the region 240mμ to 300mμ. Changes in the environments of casein (
e. g., pH, medium, temperature) caused some alterations in the absorption spectrum of casein.
(1) The maximum absorption of UV absorption spectra of casein was shifted from 278mμ at pH 6.81 and pH 10.30 to 284mμ at pH 11.21 and 292mμ at pH 12.40. The minimum absorption was shifted from 251mμ at pH 6.81 to 256mμ at pH 10.30, 271mμ at pH 11.21 and 274mμ at pH 12.40. These red shifts were accompanied with hyperchromic effects.
(2) When 20m
M or 40m
M NaCl was added to salt free casein solution, red shift and hyperchromic effect were observed in the difference spectrum. This alteration was characterized by 3 peaks at 280, 287 and 293mμ.
(3) When urea was added to salt free casein solution, urea denaturation blue shift was observed in the difference spectra. Hypochromic effect, which was characterized by 3 peaks at 280, 288 and 293mμ, was observed. The urea corc. dependence of ΔO. D. at 288mμ and 293mμ were in proportion to 0.5
M_??_4.0
M urea.
(4) The effects of temperature on the difference spectrum of casein were accompanied with red shift. Difference peaks at 287mμ and 293mμ were observed by elevated temperature from 15°C to 70°C.
(5) It was observed that the alterations of the difference spectrum of casein by environmental changes of NaCl, urea and temperature were characterized by configurational changes of tyrosine residue and tryptophane residue.
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