Phytochrome의 활성형인 Pfr과 불활성형인 Pr의 단백질 표면에 있는 소수성 부위를 $alpha$-chymotrypsin에 의한 부분가수분해와 SDS에 의한 변성으로 연구하였다. Phytochrome을 효소와 60:1 (w/v)의 비율로 가수분해 할때 Pr형의 660 nm 흡광도는 20%가 감소하는 반면 Pfr 형의 730 nm 흡광도는 완전히 소멸하였다. $alpha$-chymotrypsin의 가수분해물을 SDS-gel 전기영동으로 검정한 peptide 양상으로 보아서 Pr형이 가수분해속도가 빠르지만 단백질표면의 소수성 부위 는 Pfr 형에서 더욱 다양하게 분포되어 있었다. $alpha$-Chymotrypsin 가수분해의 초기 생성물인 chromopeptide는 non-chromopeptide보다 가수분해 속도가 느리게 나타났다. Pfr 형이 Pr형에 비하여 가수분해 속도가 느림에도 불구하고 흡광 spectrum이 급격히 변화하는 것은 Pr 형에서 Pfr형으로 광전환 할때 단백질과 색소의 결합주변에 소수성 부위가 생성되었기 때문이고 이 소수성 부위는 phytochrome의 활성부위와 관련이 있을 것으로 생각되었다.
The nature of hydrophobic sites on the protein surfaces of the Pr and Pfr forms of phytochrome (118 kDa) has been studied by spectroscopic and electrophoretic properties of phytochrome that was partially digested with $alpha$-chymotrypsin. The enzyme digestion bleached the Pfr spectrum completely at a 1:60 (w/v) enzyme to substrate ratio, while the Pr absorbance was decreased by 20%. SDS-gel electrophoresis of the $alpha$-chymotrypsin-digested phytochrome showed that, at an early stage of digestion, the rate of hydrolysis was faster in the Pr form and the electrophoretic pattern of polypeptide digests was more complicated in the Pfr form than in the Pr form. The chromopeptide domain was more resistant to $alpha$-Chymotrypsin digestion than the nonchromophore domain. The pronounced susceptibility of the Pfr spectrum to $alpha$-Chymotrypsin was considered to be the action of the enzyme on hydrophobic site(s) at the chromophore vicinity that was newly developed by phototransformation from the Pr form to the Pfr form.
