Determination of Extinction Coefficients of Oat Phytochrome by Quantitative Amino Acid Analyses

Abstract

Previously published extinction coefficients for phytochrome were based on indirect colorimetric estimates of protein weight, mostly by the Lowry method, using bovine serum albumin as a standard. This paper reports revised values based on quantitative amino acid analyses of highly purified phytochrome. The molar extinction coefficient of the red-absorbing form of phytochrome with 120000mol. wt subunits was found to be approximately 102000cm-' per 120000mol. wt at 667nm. The molar extinction coefficients at 667 nm for phytochrome with 120000 mol. wt subunits and for the 60000 mol. wt chromopeptide of P, were found to be approximately the same for samples of equivalent purity. Included in the amino acid analyses of phytochrome with 120000 mol. wt subunits are values for cysteine (1 1) and cystine (I), measured by two different techniques that gave the same results and agreed well with the estimate of total half-cystine (14) obtained by an independent method. Tryptophan was quantitated by analysis of a p-toluene sulfonic acid hydrolysate.

Photochemistry of 124 Kilodalton Avena Phytochrome In Vitro

“…The value of 7.5 x I07 cm2 mol-' for the Pr form of 118/114 kD phytochrome agrees well with previous determinations using the Lowry assay for phytochrome preparations of similar purity (14,16). However, Roux et al (14) The data presented here provide further evidence that the 6 to 10 kD peptide segment(s) proteolytically cleaved from the 124 kD molecule are critical in maintaining the molecular integrity of native phytochrome. Understanding how these segment(s) affect Pr --.…”

Modulation of oat mitochondrial ATPase activity by CA2+ and phytochrome.

“…The exogenous phytochrome was comprised mainly of 118,000 D phytochrome. But (30), it is possible that some 124,000 D phytochrome was present in the population ofexogenous phytochrome molecules used. This study, then, does not rigorously determine whether the peptide removed in the degradation of 124,000 D phytochrome to 118,000 D phytochrome is required for the ATPase effects shown here.…”

A red-green photochromic bacterial protein as a new contrast agent for improved photoacoustic imaging

“… [10] , [11] , [12] These receptors have several advantages for photoacoustic imaging since they have low fluorescence yields (typically 10 −2 -10 −3 ) [13] and high molar absorption coefficients (85,000–110,000 M −1 cm −1 ). [14] , [15] , [16] To further improve such applications such as contrast increase in photoacoustic imaging, reversibly switchable fluorescent proteins have been employed. [11] , [17] , [18] .…”