Oxidative Activity of Cytoplasmic Particles of Apples: Electron Transfer Chain

Abstract

PLANT INDUSTRY STATION, BEI TSVILLE, MARYLANDSome recent studies of apple respiration by Hackney (8) implied that the fruit may mediate its oxidations through a phenol oxidase system. In a later study Webster (21,22) could find no evidence for a cytochrome oxidase system in apple tissue. However, more recently a number of reports have appeared which demonstrated cytochrome oxidase activity in apple tissue slices (14) and in cytoplasmic particles from apples (13,16). There are also data showing Krebs cycle activity in cytoplasmic particles from apples (9,18). Nevertheless, a number of workers are still experiencing considerable difficulty in isolating active cytoplasmic particles from apples (15). The difficulties might be traced to characteristics of the apple fruit, such as a highly acid cell sap (pH 3.5), an extremely low concentration of protein (approximately 0.3 %), and a high concentration of polyphenol substances that may injure cytoplasmic particles during homogenization. As a first step in isolating active cytoplasmic particles from such tissues it seemed advisable, as previously noted (13) controlled with a variac. The homogenates were strained through four layers of cheesecloth and centrifuged for 10 minutes at approximately 1,000 X G followed by a high speed centrifugation of the supernatant at about 17,000 X G for 15 minutes. The particles obtained from the high speed centrifugation were washed in 0.25 M sucrose and resedimented at 17,000 X G. The particles were finally suspended in 6 ml of 0.25 M sucrose and 0.001 M adenosine triphosphate (ATP) adjusted to pH 7.0. These suspensions generally had a nitrogen (N) content (N of ATP subtracted) that varied from 250 to 900 Ag/ml depending on the buffer of the homogenizing medium. All operations were carried out in a cold room held at 2 to 40 C.ASSAY PROCEDURES: Spectrophotometric assays were conducted at room temperature (approx 20°C) with a Beckman DU spectrophotometer in cuvettes of

Preparation and Properties of Sweet Potato Mitochondria

“…The mechanism of inhibition remains unknown (17). The loss of antinmycin A inhibition caused by degradation of the inhibitor h1as been reported (28 (25) 298 (36) 288 (38) reported here fall within the range of those reported (23) for lupine mitochondria. VIII.…”

“…The inhibitions parallel one aniother but concentrations higlher than those recor(ledI for plant mitochondria (22,28) were required.…”

Comparison of Mitochondria from Tomato Fruits at Various Stages of Ripeness

“…The pH had little effect on green preparations, but ripe preparations were extremely sensitive to pH 6.5. The effect was not due to increased extraction of nitrogen at the low pH which might be expected on the basis of results from isolation of apple mitochondria (10). Isolation of ripe mitochondria at pH 8.4 did not give significantly greater oxidative activity than isolation at pH 7.5, and phosphorylation was adversely affected by the higher pH.…”

Oxidative activity of cytoplasmic particles of apples: Krebs cycle oxidations, oxidative phosphorylation, & cytochromes

“…SPECTRA OF PARTICLES: The relatively high concentration of chlorophyll andI lowv concentrationi of cytochromes miiade it (lifficult to observe spectra of cvtochromes in apple particles (13 The absorption bands were more clearly defined by studying spectra of acetone-extracted particles at liquid-nitrogen temperatures (-195 C). At -1950 the cytochromie spectra are intensified and given greater detail as shown by a number of workers with plant mitochondria (9, 2, 3, 1).…”

“…Previous studies of procedures for isolating apple mitochondria showed the importance of pH during homogenization of the tissues (12,13). Virtually no mitochondrial activity could be detected in particles from neutral homogenates.…”