Effects of 5-bromo-2'-deoxyuridine on Friend erythroleukaemia cells. II. Oxidative metabolism and enzyme content of whole cells and isolated mitochondria.

Untreated or bromodeoxyuridine (BrdUrd)-treated Friend erythroleukaemia (EL) cells from 15- and 72-h-cultures were harvested and the mitochondria were isolated by homogenization and differential centrifugation. Aliquots of the original cell suspensions or the final mitochondrial suspensions were either fixed for electron microscopy, assayed for enzyme activities, or introduced into a 1-ml Clarke oxygen electrode chamber. Whole BrdUrd-treated cells exhibited notable morphological alterations (see accompanying paper) but no effect was observed on whole-cell respiration. Morphologically, isolated mitochondria exhibited a highly condensed matrix and a greatly expanded outer compartment. Functionally, these mitochondria oxidized a variety of substrates at high state-3 (ADP-stimulated) rates (60-210 ng atoms O/min per mg protein) and displayed adequate respiratory control and ADP/O ratios. In the mitochondria isolated from BrdUrd-treated EL cells (both 15- and 72-h cultures), the state-3 oxygen consumption rates, respiratory control ratios, and ADP/O ratios generally decreased compared to their matched controls. These functional deficiencies coincided with in situ increases in the volume of the mitochondrial compartment and conspicuous (30-100%) increases in the specific and total activities of several mitochondrial enzymes. In addition, the mitochondria isolated from the 72-h group (treated and untreated) displayed immediate alterations when BrdUrd was added to the electrode chamber. Oxygen consumption rates dropped, respiratory control ratios changed moderately, and ADP/O ratios increased. BrdUrd may act both as an inhibitor of oxidative phosphorylation and perhaps as a sink for some of the high energy phosphate that is being generated. Thus, BrdUrd may exert its inhibitory effect on cell differentiation by interfering with mitochondrial function.