The influence of temperature on glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase and the regulation of these enzymes in a mesophilic and a thermophilic cyanobacterium

✍ Scribed by Henk J. Lubberding; Peter V. M. Bot

• Publisher: Springer
• Year: 1984
• Tongue: English
• Weight: 645 KB
• Volume: 137
• Category: Article
• ISSN: 0302-8933
• DOI: 10.1007/bf00414450

✦ Synopsis

The activities and kinetics of the enzymes G6PDH (glucose-6-phosphate dehydrogenase) and 6PGDH (6-phosphogluconate dehydrogenase) from the mesophilic cyanobacterium Synechococcus 6307 and the thermophilic cyanobacterium Synechococeus 6716 are studied in relation to temperature. In Synechococcus 6307 the apparent K~'s are for G6PDH: 80gM (substrate) and 20gM (NADP+); for 6PGDH: 90gM (substrate) and 25gM (NADP+). In Synechococcus 6716 the apparent Km's are for G6PDH: 550gM (substrate) and 30gM (NADP+); for 6PGDH: 40 gM (substrate) and 10 gM (NADP +). None of the Km's is influenced by the growth temperature and only the Km's of G6PDH for G6P are influenced by the assay temperature in both organisms. The idea that, in general, thermophilic enzymes possess a lower affinity for their substrates and coenzymes than mesophilic enzymes is challenged.

Although ATP, ribulose-l,5-bisphosphate, NADPH and pH can all influence the activities of G6PDH and 6PGDH to a certain extent (without any difference between the mesophilic and the thermophilic strain), they cannot be responsible for the total deactivation of the enzyme activities observed in the light, thus blocking the pentose phosphate pathway.