Isoenzyme degradation

In this report we describe the kinetics of pectate and pectin degradation by Eca PL isoenzymes. Moreover, action pattern analyses using various pectic substances provide further insights into specific differences among the isoenzymes. 

An intriguing environmental feature of an Eca invasion in potatoes is the change from pH 5.0 in fresh tissue to pH 8.5 in the infected tissue after 72 h. We propose that the involvement of PLs in the degradation of pectin is an evolutionary consequence of the alkalinization which inactivates PG [optimal activity for Eca PG is at pH 6.0 (unpublished results)]. Moreover, secretion of PL isoenzymes may ensure successful biological activity of Eca in diverse types of host cell walls. 

Wegener, C., Bartling, S., Olsen, O., Thomsen, K.K., Bahlow, R. and von Wettstein, D. Differences in cell wall degradation patterns by Erwinia carotovora pectate lyase isoenzymes. Submitted to Protoplasma. 

Wegener C, Battling S, Olsen O, Thomsen KK, Bahlow R, von Wettstein D (1995) Differences in cell wall degradation by Erwinia carotovora pectate lyase isoenzymes. Prep, for publication. 

The mechanism of metabolic degradation of indol-3-ylacetic acid (39) is a matter of debate. A possible route demonstrated in vitro includes oxidative decarboxylation to skatolyl hydroperoxide (40), catalyzed by horseradish peroxidase isoenzyme C (HRP-C), followed by rearrangement to 3-(hydroxymethyl)oxindole (41), as shown in equation 12 . 

Phosphodiesterases are a group of enzymes that, among other actions, hydrolyse cAMP. Phosphodiesterase inhibitors are selective for phosphodiesterase III (PDE-III) isoenzyme present in the heart. They prevent the degradation of cAMP, thereby increasing its intracellular concentration (Figure 8.4). This leads to an increase in the intracellular concentration of Ca2+ and an increased contractility and heart rate. PDE-III inhibitors have no adrenoceptor agonistic activity and therefore can be used in combination with other sympathomimetic drugs. They also increase cAMP levels in vascular smooth muscle, but this results in lower intracellular Ca2+ concentrations and thus vasodilatation. 

---