Triosephosphate isomerase from baker's yeast - ribozyme versus protein

• Main Author: ON Solovjeva (Author)
• Format: Book
• Published: Open Journal of Analytical and Bioanalytical Chemistry - Peertechz Publications, 2020-08-18.
• Subjects: Research Article
• Online Access: Connect to this object online.

<p>It was previously shown that in baker's yeast Saccharomyces cerevisiae, transketolase can exist not only free, but in complex with RNA. The complex does not possess transketolase activity [N.K. Tikhomirova, G.A. Kochetov, A new method of isolation and a new form of transketolase from baker's yeast, Biokhimiia 56 (1991) 1123-1130]. </p><p>We discovered that this RNA is a ribozyme which catalyzes the interconversion of glyceraldehyde 3-phosphate (G3P) and dihydroxyacetone 3-phosphate (DHAP), i.e. acting as triosephosphate isomerase (TPI). It also catalyzes an unusual reaction of ribose 5-phosphate (R5P) decomposition to G3P ​​and erythrose. TPI-ribozyme was found in baker's yeast not only in complex with transketolase, but also in free form. Transketolase-RNA complex was easily isolated on an immunoaffinity column with antibodies to transketolase. TPI-ribozyme consists of 87 nucleotides and has a molecular weight of 26.6 kDa. The optimum of pH-activity is 7.5 for DHAP, 6.7 for R5P and 9.0 for G3P. Km and Vmax are accordingly 0.29 mM and 2.6 U/mg for DHAP, 22 mM and 0.65 U/mg for R5P, 0.05 mM and 4.3 U/mg at pH 7.6 and 0.11 mM and 16 U/mg at pH 9.0 for G3P. These kinetic characteristics are the same for free RNA and in the complex with transketolase. Ki for RNA binding to transketolase was 1.0 μM. Accordingly, the TPI-ribozyme performs a dual function - it shows TPI activity and blocks the work of transketolase, thereby switching the metabolic process to glycolysis. The location of the TPI-ribozyme gene is determined. Blocking the activity of transketolase by ribozyme may be of practical importance in medicine, particularly, in cancer therapy.</p>