Partial purification and kinetic characterization of a carotenoid cleavage enzyme from quince fruit (Cydonia oblonga)

For the first time, a cytosolic carotenoid cleavage enzyme isolated from quince (Cydonia oblonga) fruit is described. The enzyme was partially purified by using centrifugation, acetone precipitation, ultrafiltration (300 kD, 50 kD), isoelectric focusing (pH 3-10), and sodium dodecyl sulfate polyacrylamide gel electrophoresis (7.5%). In this way, an enzymatically active protein fraction was obtained that contained three similar proteins, all exhibiting molecular weights in the range of 20 kD. Using beta-carotene as substrate, the enzyme activity was detected spectrophoto metrically at a wavelength of 505 nm. The time constant of the reaction was 8.2 min, the Michaelis constant (K-m) was 11.0 mumol(.)L(-1), and the maximum velocity (v(max)) was 0.083 mumol(.)L(-1.)min(-1.)Mg((protein))-1. The optimum temperature was above 50 degreesC.