Enzymes activity, variations during

Figure 2. Temporal profile of DDC enzyme activity during Drosophila development. Note the major peaks of DDC induction during late embryo-genesis, at pupariation, and at the time of eclosion of the adult from the pupal case. At these developmental times when there is extensive synthesis and hardening of cuticle, the induced DDC in the hypoderm is involved in this process. Levels of DDC in the CNS show much less developmental variation (Hirsh, 1986). Figure adapted from Hirsh, 1986.

FIGURE 12-43 Variations in the activities of specific CDKs during the cell cycle in animals. Cyclin E-CDK2 activity peaks near the G1 phase-S phase boundary, when the active enzyme triggers synthesis of enzymes required for DNA synthesis (see Fig. 12-46). Cyclin A-CDK2 activity rises during the S and G2 phases, then drops sharply in the M phase, as cyclin B-CDK1 peaks. 

Induction occurs predominantly at the level of transcription (Fig. 1), often being regulated by specific receptors that interact with the chemical inducer (Fig. 2 Table 1). During the last decade it has become feasible to study the impact, on DME expression, of polymorphisms in regulatory factors in addition to genetic variation in coding regions of enzymes themselves. In a few instances, elevation of enzyme level and enzyme activity is... 

The pronounced effects of pH on enzyme reactions emphasize the need to control this variable by means of adequate buffer solutions. Enzyme assays should be carried out at the pH of optimal activity, because the pH-activity curve has its minimum slope near this pH, and a small variation in pH will cause a minimal change in enzyme activity. The buffer system must be capable of counteracting the effect of adding the specimen (e.g, serum itself is a powerful buffer) to the assay system, and the effects of acids or bases formed during the reaction (e.g., formation of fatty acids by the action of lipase). Because buffers have their maximimi buffering capacity close to their pK values, whenever possible a buffer system should be chosen with a pK value within IpH unit of the desired pH of the assay (see Chapter 1). Interaction between buffer ions and other components of the assay system (e.g., activating metal ions) may eliminate certain buffers from consideration. 

The oscillations of fig. 2.14 correspond to a periodic variation of the enzyme activity, which passes from less than 1% to some 75% of the maximum reaction rate (fig. 2.15). This range is comparable to that observed in the course of glycolytic oscillations in yeast for the periodic variation in PFK activity (Hess et al, 1969). As indicated in table 2.2, the mean value and the maximum reached by the enzyme activity during oscillations depend on the value of the substrate injection rate. 

Several samples were taken during the exponential and stationary phases and used for measurement of different parameters such as enzyme yield, cell density, plasmid copy number, and plasmid stability. The optimal enzyme production for all strains was found to be in one of the samples from the stationary growth phase. The obtained maximum cell density varied for the different yeast strains when grown in shake flasks and the enzyme activity data have therefore been corrected for variation in the cell density (Figure 4). The preliminary results from these studies indicate that it is possible to find host systems that are better producers of enzymes than... 

As shown in Fig. 1, poly(ADP-ribose) transferase activity in lizard oviduct nuclei undergoes a marked variation during the reproductive cycle. An increase in poly(ADP-ribose) transferase activity was observed at the begiiming of the recovery phase (die middle of March-April) widi the peak (12 times the activity detected during the reproductive stasis and secretory period) about the first week of May after the oviduct had reached its maximum growth and was ready to be functional. Oviduct growth followed the increase in poly(ADP-ribose) transferase activity. Enzyme activity in... 

Fig. 5. Variation of levels of enzyme activity during growth of cultured cells of N. silvestris. Dashed line indicates transfer of cells in late-exponential growth to fresh medium (16-fold dilution). Data shown at the upper right is a portion of a growth curve obtained between 30 and 32 generations of continuous exponential growth. The bottom section shows specific activities (nmoles/min/mg) obtained for DAHP synthase-Mn [DS-Mn], DAHP synthase-Co [DS-Co], and arogenate dehydrogenase [AGN DH] in samples taken from cultures at times (in days) aligned with the values of specific activity.

Fig. 3.7. The diurnal variation of PEP carboxylase (PEP) and malate enzyme (ME) in a cactus, Nopalea dejecta. PEP carboxylase activity is high during acidification and malate enzyme is high during deacidification. Assay run on preparations which were not desalted or otherwise treated (data of Mukerji, Ind. J. Biochem. Biophys. 5, 62-63, 1968, by permission)...

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