PubMed · 407396
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
N Ben-Shalom, V Kahn, E Harel, A M Mayer. 1977. Olive catechol oxidase-changes during fruit development.. https://doi.org/10.1002/jsfa.2740280612
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
A study of the catecholase activity of a latent plant polyphenol oxidase, extracted and purified from the chloroplast membranes of grapes (Vitis vinifera cv. Airen), revealed for the first time a lag phase above pH 5.0, whereas a steady-state rate was reached immediately when pH values were lower, thus suggesting the hysteretic nature of the enzyme. During steady state, the enzyme showed negative co-operativity concomitant with the presence of the lag period, and followed classical Michaelis-Menten kinetics under more acid pH conditions. Statistical analysis of these data showed a minimal value for the extreme Hill coefficient of 0.54 at pH 6.0. This kinetic behaviour of polyphenol oxidase has been interpreted in terms of the pH-induced 'slow' transition mechanism reported by Ricard, Noat & Nari [(1984) Eur. J. Biochem. 145, 311-317] in which the conformational change does not affect the active site of the enzyme.
A new approach to the study of enzyme activity in organic solvents has been developed by using optically transparent reverse vesicles. Polyphenol oxidase was incorporated in an active form into the above ternary system formed by the non-ionic surfactant tetra(ethylene glycol) dodecyl ether/n-dodecane/water. The enzyme in this microenvironment, surprisingly, showed an apparent positive co-operativity which has never before been described either in aqueous solution or in reverse micelles. In addition, the Vmax. expressed was similar to that in water and twice that displayed in reverse micelles.
The melanocytes are acutely sensitive to a single pulse of UV and express neural differentiation. The present work was undertaken to observe whether the melanocyte can sense variations in the duration of UV exposure. Whole skin organ cultures from marginal zone in vitiligo were exposed to a single pulse of UV, 30, 60, 90 and 120 s each. Catecholoxidase levels in the marginal melanocytes and the volume of melanocytes were used to calculate and quantitate the changes in enzyme production. The melanocytes' dendricity, volume and enzyme production increases with the duration of UV exposure. This sensitivity of the marginal melanocytes, to changes in the duration of UV exposure, simulates the coat color changes in weasels and the polar fox exposed to extreme variations in the day/night cycles. The UV response is associated with proliferation of melanocytes as it is G2-phase dependent. Thus the melanocytes form a UV-sensitive neural network responding to annual changes in the photoperiodicity.