Abstract
1. 1. The enzyme D- glycero D- ido octulose l,8-bisphosphate:D- altro-heptulose 7-phosphotransferase (abbreviated to phosphotransferase, PT) catalyses the transfer of the phosphate ester group at C-l between altro-heptulose (sedoheptulose) and octulose phosphate intermediates of the L-type pentose pathway. 2. 2. Using synthetically prepared and 14C-labelled octulose mono- and bisphosphates, two methods are described for the measurement of the catalytic capacity of the PT reaction operating in both the “forward” and “reverse” modes of L-type pentose pathway operation. 3. 3. PT activity was found in normal, regenerating and foetal rat liver, rat heart, rat epididymal fat pad, rat kidney, brain and skeletal muscle, extracts of C. fusca, pea leaf and a variety of tumour tissues. 4. 4. The highest activity of the enzyme was found in the neoplasms. 5. 5. The Michaelian kinetic constants, temperature and pH optima for the reaction of the enzyme from rat liver together with an assortment of its substrate specificities have been determined. 6. 6. Vanadate anion was found to inhibit the enzyme and the pattern of inhibition suggests that the PT may act by a sequential mechanism. 7. 7. Neither arabinose 5-phosphate nor inorganic phosphate showed any effect on the catalytic activity of the PT enzyme in liver.
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