Download Proteins Made in Mitochondria of Cultured Animal Cells

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BIOCHEMICAL SOCIETY TRANSACTIONS
with thoseofthepentosephosphatepathway;thelatterenzymes in turnall have thesame
phase. A similar pattern seems possible in Acer.
With enzyme activities (and to a smaller extent with the metabolite concentrations)
there was a gradual damping of the oscillations over a period of 3-4 days. In contrast the
rhythm in the rate of O2 uptake, which was recorded every 6h during the transition,
showed no evidence of damping out. Its amplitude (about one-third of the total uptake
rate) and frequency (18 h) remained constant throughout the transition period.
As might possibly have been expected, fluctuations in the concentrations of key metabolites occurred concomitant with oscillations in enzyme activities. Oscillations of high
amplitude were noted for key cofactors such as ATP. Smaller but similar oscillations were
observed for a range of other metabolites (Fig. 2).
An immediate question arising from the findings described here is whether metabolic
oscillations also occur during steady-state growth. In previous studies, with continuous
cultures of sycamore cells, the time-interval between assays was 48h, compared with
only 6h in the present work. I t is therefore unlikely that oscillations would have been
detected in the previous experiments.
The occurrence of rhythmic oscillations in both enzyme activities and metabolite
concentrations is a complicating factor in the study of the regulation of plant cell metabolism. As such, these phenomena need to be thoroughly investigated before studies on
regulatory mechanisms are performed.
This work was supported by S.R.C. Grant B/RG/2093 to M. W. F.
Bergmeyer, H. U. (ed.) (1963) Methods of Enzymaric Analysis, Academic Press, New York and
London
Chance, B.. b e , E. K., Ghoch, A. K. & Hess, B. (eds.) (1973) EiologicalandEiochemicalOscillators, Academic Press, New York and London
Dietzer, G. F., Kempf, O., Fischer, F. & Wagner, E. (1974) Planta 117, 29-41
Fowler, M. W. & Clifton, A. (1974) Eur. J. Eiochern. 45, 445-450
Hartree, E. F. (1972) Anal. Biochern. 48,422-450
Sarkissian; G. S. S. & Fowler, M. W. (1974) Planta 119, 335-349
Wilson, S. B., King, P. J. &Street, H. E. (1971)J. Exp. Bot. 22, 177-207
Proteins Made in Mitochondria of Cultured Animal Cells
ALEC JEFFREYS and IAN CRAIG
Genetics Laboratory, Department of Biochemictry, Uiriversity of Oxford,
South Parks Road, Oxford 0X1 3 Q U, U.K .
["SIMethionine incorporation into cultured human or mouse cells in the presence of an
inhibitor of cytoplasmic protein synthesis (emetine or cycloheximide) has been shown
to reside principally in some eight or nine labelled polypeptides. These can be resolved
by electrophoresis of whole-cell extracts on slab polyacrylamide gels containing sodium
dodecyl sulphate. Chloramphenicol, an inhibitor of mitochondrial ribosomes (see
Ekattie, 1971), specifically inhibits the synthesis of these proteins, suggesting that they
represent products of mitochondrial protein synthesidin vivo (Jeffreys & Craig, 1974).
We have suggested that these proteins may serve as markers of the mitochondrial
genome in interspecies somat ic-cell hybrids. Several human-mouse hybrids, which retained between 8 and 11 human chromosomes, were found to synthesize only mouse
'mitochondrial' proteins. This would be expected if the expression of the human mitochondrially synthesized proteins was dependent on the presence of human mitochondrial DNA. However, non-random segregation of human chromosomes could also
give rise to a similar observation. Two independent studies have failed to detect human
mitochondrial DNA in human-mouse hybrids that haveeliminated a substantial number
of human chromosom-- (Clayton e ta l. , 1971 ; Attardi & Attardi, 1972), whereas Coon
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555th MEETING, ABERYSTWYTH
399
et al. (1973) obtained hybrids retaining high proportions of both rodent and nuclear
genomes, some of which also retained human and rodent mitochondrial DNA.
We have extended our studies on the nature of proteins synthesized in.the presence of
cycloheximide (or emetine) and examined gel-radioautographic profiles of putative
mitochondrial proteins from cell lines of several mammalian species, employing the techniques previously described (Jeffreys & Craig, 1974). Although the overall number and
distribution of labelled proteins remained about the same, characteristic differences
between some of the species were resolved: the patterns obtained with rat and mouse cell
lines were extremely similar, but both could be distinguished from those obtained with
rabbit or Chinese-hamster cell lines.
Further evidence of the mitochondrial nature of these proteins has been obtained by
fractionation of human HeLa B cells, labelled in vivo in the presence of cycloheximide.
The chloramphenicol-sensitivelabel was found to follow closely the activity of cytochrome c oxidase (a mitochondrial inner-membrane marker) when extracts were subjected to sucrose-density-gradient centrifugation. Labelled mitochondria purified from
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Fig. 1 . Microdensitometer trace recordings of the radioautographs obtained afrer electrophoresis of human or mouse cells labelled with [3SS]metl~ionine
or [L4C]leucinein the presence of 5Opg of emetinelml
Human cells (D98) were labelled (a) with [35S]methionine and (b) with ['4C]leucine.
Mouse cells (RAG; Klebe et al., 1970) were labelled (c) with [3sS]methionine and ( d )
with ['4C]leucine. [3SS]Methionine incorporation is described elsewhere (Jeffreys &
Craig, 1974). Incorporation of [14C]leucine(The Radiochemical Centre, Amersham,
Bucks., U.K.) was similarly performed in minimal essential medium (lacking leucine)
supplemented with Earle's salts (Bio-Cult Laboratories Ltd., Paisley, U.K.) plus 10%
(v/v) 'foetal calf serum dialysed against Earle's salts.
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BIOCHEMICAL SOCIETY TRANSACTIONS
the gradient were shown by electrophoresis to contain a full profile of the putative
mitochondrially synthesized proteins seen in whole-cell extracts.
Similar patterns were observed from cells labelled for either 30min or 5 h in the presence of emetine. The spectrum of proteins synthesized by mitochondria thus does not
appear to alter with time after the addition of inhibitor. Further, the profile of human
mitochondrial proteins of cells labelled in the presence of cycloheximide for 4 h was
similar to that obtained after a subsequent 3 h post-incorporation release from the inhibitor in the absence of labelled methionine. This suggests that interconversion and
degradation of the mitochondrially made proteins does not occur to a significant extent.
Gel profiles of the products of mitochondria1 protein synthesis from human or mouse
cells labelled with ['4C]leucine were qualitatively similar to those obtained by labelling
with [35S]methionine, except that one minor labelled protein seen in the human 35S
profile appeared to be absent from the I4C pattern (see Fig. 1). The detection of interspecies differences thus does not depend on the usc of methionine as the labelled amino
acid and cannot result from the incorporation of the radioactive sulphur into nonprotein components that might possibly be detected with the analytical system employed.
A. J. is the recipient of a Christopher Welch Scholarship.
Attardi, B. & Attardi, G. (1972) Proc. Nut. Acad. Sci. US.69, 129-133
Bcattie, D. S. (1971) Sub-Cell. Biochem. 1, 1-28
Clayton, D. A., Teplitz, R. L., Nabholz, M., Dovey, D. & Bodmer, W. F. (1971) Nature
(London) 234,560-562
Coon, H. G., Horak, I. & David, I. B. (1973) J. Mol. Biol. 81, 285-298
Jeffreys, A. & Craig, I. (1974) Biochem. J. 144, 161-164
Klebc, R. J., Chen, T. R. & Ruddle, F. H. (1970) J. Cell Biol. 45, 7482
Regulation of Pyruvate Kinase from the Hepatopancreas of the Crab
Carcinus maenas
IAN G. GILES, PETER C. POAT and KENNETH A. MUNDAY
Department of Physiology and Biochemistry, University of Southampton,
Southamptoti SO9 5NH,U.K.
I n common with mammalian gluconeogenic tissues the hepatopancreas of the common
shore crab, Carcinus maenas, contains a high activity of pyruvate kinase but a relatively
low activity of pyruvate carboxylase. I n Carcinus the activity of the former exceeds that
of the latter by approximately 5-fold when both enzymes are measured under maximum
rate conditions. In order to obtain a net synthesis of phosphoenolpyruvate one would
therefore expect that the activity of pyruvate kinase in uivo is likely to be diminished to
below that of pyruvate carboxylase. This possibility was investigated by using the
effectors of pyruvate kinase at concentrations that approximate to those found under
physiological conditions.
The activity of pyruvate kinase was measured by the method of Bucher & Pfleiderer
(1955), except that 25rn~-Tris-HCI,pH7.4, was used as a buffer and the concentration
of free Mgz+was maintained at 5 m by~ adding the calculated amount of MgCI2 to the
assay mixture, which contained ~Om~-dipotassium
glycerol I-phosphate (Boyer, 1969).
This salt was also the source of K+. The oxidation of NADH was followed at 340nm in a
Perkin-Elmer model 356 dual-wavelength spectrophotometer at 25°C. Solutions of
ADP, ATP, phosphoenolpyruvate and fructose 1,6-diphosphate were prepared each
day and assayed enzymically to determine their concentrations before use.
Hepatopancreas pyruvate kinase was purified to a specific activity of 160 (pmol of
NADH oxidized/min per mg of enzyme at 25°C) and was essentially homogeneous as
judged by polyacrylamide-gel electrophoresis. At low phosphoenolpyruvate concentrations fructose 1,6-diphosphate was an activator of theenzyme. In the absence of the latter,
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