Characterization of two d‐glyceraldehyde‐3‐phosphate dehydrogenases from the extremely thermophilic archaebacterium Thermoproteus tenax

Abstract

Thermoproteus tenax possesses two different glyceraldehyde‐3‐phosphate dehydrogenases, one specific for NADP+ and the other for NAD+. NADP(H) inhibits the NAD+‐specific enzyme competetively with respect to NAD+ whereas NAD(H) virtually does not interact with the NADP+‐specific enzyme. Both enzymes represent homomeric tetramers with subunit molecular masses of 39 kDa (NADP+‐specific enzyme) and 49 kDa (NAD+ ‐specific enzyme), respectively. The NADP+‐specific enzyme shows significant homology to the known glyceraldehyde‐3‐phosphate dehydrogenases from eubacteria and eukaryotes as indicated by partial sequencing. The enzymes are thermostable, the NADP+‐specific enzyme with a half‐life of 35 min at 100°C, the NAD+ ‐specific enzyme with a half‐line of ≥20min at 100°C, depending on the protein concentration. Both enzymes show conformational and functional changes at 60 – 70°C. Copyright © 1987, Wiley Blackwell. All rights reserved