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Sequential transfer of derepressing yeast spheroplasts from a medium containing chloramphenicol to one containing cycloheximide or vice versa, shows that the cytosolically and mitochondrially synthesized products are synthesized independent of each other and accumulate in the absence of their counterparts. This has been demonstrated by immunoprecipitation using specific antisera for cytochrome oxidase and ATPase enzymes. The independently accumulated products have been shown to complement each other for the expression of enzyme activity, upon mixing in vitro. By varying the time of treatment with cycloheximide, thereby allowing the mitochondrial protein synthesis to proceed to different extent, a time sequence in the appearance of the mitochondrially synthesized products is demonstrated.

NATURE 577 was easily recovered, leaving no trypsin contamina-Table I. DISTRIBUTION OF COENZYME QIN RAT LIVER CELL FRACTIONS tion of the chymotrypsin; and with proper precautions, the derivative was re-usable. Similar applications could be suggested for other enzymes.

The activities of delta-aminolaevulate synthetase and delta-aminolaevulate dehydratase have been assayed in Saccharomyces cerevisiae during glucose repression and de-repression. delta-Aminolaevulate dehydratase increased concomitantly with the increase in oxygen uptake during the de-repression phase caused by the depletion of glucose in the medium. delta-Aminolaevulate synthetase showed an oscillatory behaviour and a spurt in its activity always preceded the increase in oxygen uptake. The activity of both the enzymes was lowered if the cells were incubated with glucose or cycloheximide, but not with chloramphenicol.