Proteolysis alters the spectral properties of 124 kdalton phytochrome fromAvena
✍ Scribed by Richard D. Vierstra; Peter H. Quail
- Book ID
- 104754968
- Publisher
- Springer-Verlag
- Year
- 1982
- Tongue
- English
- Weight
- 968 KB
- Volume
- 156
- Category
- Article
- ISSN
- 0032-0935
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✦ Synopsis
Native phytochrome from Arena sativa L. is homogeneous with a monomeric molecular weight of 124 kdalton; 6-10 kdalton larger than the heterogeneous "120" kdalton preparations previously considered to be undegraded (Vierstra and Quail, 1982, Proc. Natl. Acad. Sci. USA, 79: 5272-5276). The phototransformation difference spectrum (Pr-Pfr) of 124 kdalton phytochrome measured in crude extracts has a minimum in the farred region at 730 nm, the same as that observed in vivo. These spectral properties contrast with those of "120" kdalton phytochrome purified by column immunoaffinity chromatography where the difference minimum is at 724 nm. When 124 kdalton phytochrome is incubated as Pr in crude extracts, the difference minimum shifts progressively to shorter wavelengths (from 730 to 722 nm) concomitant with the proteolytic degradation of the chromoprotein to the mixture of 118 and 114 kdalton species that comprise "120" kdalton phytochrome preparations. These two effects are inhibited in concert by the serine protease inhibitor, phenylmethylsulfonylfluoride, and or maintenance of the phytochrome in the Pfr form. These results provide further evidence that 124 kdalton phytochrome is the native molecule in Arena and indicate that the peptide segments removed by proteolysis of the Pr form are important to the pigment's spectral integrity. The present data thus resolve the previously unsettled question of why the Pfr form of "120" kdalton phytochrome isolated by various procedures from Arena has been found to absorb at shorter wavelengths than that observed in vivo. Previous spectral studies with Abbreviations, symbols: PMSF = phenylmethylsulfonylfluoride; SDS-PAGE = sodium dodecyl sulfate polyacrylamide gel electrophoresis; Ig=immunoglobulin; zlAmini .... AAmaxi~um = phototransformation difference spectrum (Pr-Pfr) minimum and maximum; AAr/AAfr ratio = spectral change ratio "120" kdalton phytochrome preparations are open to reexamination.