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The kinetics of enzyme changes in yeast under conditions that cause

the loss of mitochondria.Chapman C, Bartley W.

1. Aerobically grown yeast having a high activity of glyoxylate-

cycle, citric acid-cycle and electron-transport enzymes was

transferred to a medium containing 10% glucose. After a lag phase of

30min. the yeast grew exponentially with a mean generation time of

94min. 2. The enzymes malate dehydrogenase, isocitrate lyase,

succinate-cytochrome c oxidoreductase and NADH-cytochrome c

oxidoreductase lost 45%, 17%, 27% and 46% of their activity

respectively during the lag phase. 3. When growth commenced pyruvate

kinase, pyruvate decarboxylase, alcohol dehydrogenase, glutamate

dehydrogenase (NADP(+)-linked) and NADPH-cytochrome c oxidoreductase

increased in activity, whereas aconitase, isocitrate dehydrogenase

(NAD(+)- and NADP(+)-linked), alpha-oxoglutarate dehydrogenase,

fumarase, malate dehydrogenase, succinate-cytochrome c

oxidoreductase, NADH-cytochrome c oxidoreductase, NADH oxidase, NADPH

oxidase, cytochrome c oxidase, glutamate dehydrogenase (NAD(+)-

linked), glutamate-oxaloacetate transaminase, isocitrate lyase and

glucose 6-phosphate dehydrogenase decreased. 4. During the early

stages of growth the loss of activity of aconitase, alpha-

oxoglutarate dehydrogenase, fumarase and glucose 6-phosphate

dehydrogenase could be accounted for by dilution by cell division.

The lower rate of loss of activity of isocitrate dehydrogenase (NAD

(+)- and NADP(+)-linked), glutamate dehydrogenase (NAD(+)-linked),

glutamate-oxaloacetate transaminase, NADPH oxidase and cytochrome c

oxidase implies their continued synthesis, whereas the higher rate of

loss of activity of malate dehydrogenase, isocitrate lyase, succinate-

cytochrome c oxidoreductase, NADH-cytochrome c oxidoreductase and

NADH oxidase means that these enzymes were actively removed. 5. The

mechanisms of selective removal of enzyme activity and the control of

the residual metabolic pathways are discussed.

PMID: 5660627 [PubMed - indexed for MEDLINE]

PMCID: PMC1198688

Inorganic nitrogen assimilation in yeasts: alteration in enzyme

activities associated with changes in cultural conditions and growth

phase.Thomulka KW, Moat AG.

Ammonia assimilation has been investigated in four strains of

Saccharomyces cerevisiae by measuring, at intervals throughout the

growth cycle, the activities of several enzymes concerned with

inorganic ammonia assimilation. Enzyme activities in extracts of

cells were compared after growth in complete and defined media. The

effect of shift from growth in a complete to growth in a defined

medium (and the reverse) was also determined. The absence of

aspartase (EC 4.3.1.1, l-aspartate-ammonia lyase) activity, the low

specific activities of alanine dehydrogenase, glutamine synthetase

[EC 6.3.1.2, l-glutamate-ammonia ligase (ADP)], and the marked

increase in activity of the nicotinamide adenine dinucleotide

phosphate-linked glutamate dehydrogenase (NADP-GDH) [EC 1.4.1.4, l-

glutamate:NADP-oxidoreductase (deaminating)] during the early stages

of growth support the conclusion that yeasts assimilate ammonia

primarily via glutamate. The NADP-GDH showed a rapid increase in

activity just before the initiation of exponential growth, reached a

maximum at the mid-exponential stage, and then gradually declined in

activity in the stationary phase. The NADP-GDH reached a higher level

of activity when the yeasts were grown on the defined medium as

compared with complete medium. The nicotinamide adenine dinucleotide-

linked glutamate dehydrogenase (NAD-GDH) [EC 1.4.1.2, l-glutamate:NAD-

oxidoreductase (deaminating)] showed only slight increases in

activity during the exponential phase of growth. There was an inverse

relationship in that the NADP-GDH increased in activity as the NAD-

GDH decreased. The NAD-GDH activity was higher after growth on the

complete medium. The glutamate-oxaloacetate transaminase (EC 2.6.1.1.

l-aspartate:2-oxoglutarate aminotransferase) activity rose and fell

in parallel with the NADP-GDH, although its specific activity was

somewhat lower. Although other ammonia-assimilatory enzymes were

demonstrable, it seems unlikely that their combined activities could

account for the remainder of the ammonia-assimilatory capacity not

accounted for by the NADP-GDH. The ability of aspartate to serve as

effectively as glutamate as the sole source of nitrogen for the

growth of yeast apparently resides in their ability to utilize

aspartate for amino acid biosynthesis via transamination.

PMID: 4400414 [PubMed - indexed for MEDLINE]

PMCID: PMC247247

Promotion of sporulation by caffeine pretreatment in Saccharomyces

cerevisiae. II. Changes in ribonuclease activity during

sporulation.Tsuboi M, Yanagishima N.

Changes in RNase activity during sporulation of a homothallic diploid

strain of Saccharomyces cerevisiae were measured in caffeine-treated

and non-treated cells. 1. In caffeine-treated cells soon after the

transfer to the sporulation medium a significant increase in RNase

activity was observed; in control cells the rise of RNase activity

was less and started after a lag period of 5 h. The final activity of

RNase activity was about twice as high in caffeine-treated cells as

in control cells. 2. Increase in RNase activity during sporulation

was sensitive to cycloheximide in control cells, but insensitive in

caffeine-treated cells. 3. RNases from vegetative cells and from

sporulating ones are different in their Km values. Relation of the

changes in RNase activity to premeiotic DNA synthesis is discussed.

PMID: 776113 [PubMed - indexed for MEDLINE]