Enzyme Activities of NADPH-Forming Metabolic Pathways in Normal and Leukemic Leukocytes

With respect to the enzymes of NADPH-forming meta-bolic pathways in human leukocytes: (a) Glucose-6-phosphate dehydrogenase and phosphogluconate dehy-drogenase (decarboxylating) were less active in leuko-cytes (mostly myeloblasts) from eight patients vith acute myeloblastic leukemia (I) than in leukocytes (mostly granulocytes) from 16 normal subjects (II) or 16 patients with chronic myelocytic leukemia (Ill). (b) Of the enzymes of the citrate cleavage pathway, ATP citrate lyase and malate dehydrogenase (decarboxylating) (NADP) were virtually absent in the cells studied. (c) lsocitrate dehydrogenase (NADP+), aspartate amino-transferase, and alanine aminotransferase, which, to-gether with the much more active malate dehydroge-nase, constitute a newly proposed NADPH-forming met-abolic cycle, showed a higher activity in I than in II or Ill, and therefore could compensate, as concerns NADPH-generation, for the low activity of pentose cycle dehy-drogenases. We are not sure whether the enzymatic characteristic of I cells is attributable to their immaturity or to their leukemic nature. AddItIonal Keyphrases: pentose phosphate pathway NADPH-forming cycle The NADPH-forming enzymes of the pentose phosphate pathway-glucose-6-phosphate dehydro-genase1 and phosphogluconate dehydrogenase decar-boxylating)-have a markedly subnormal activity in cells from cases of acute myeloblastic leukemia (1, 2), a finding that prompts further research on alterna-tive routes of NADPH-generation in such leukocytes. I Clinica Medics delI’Universit#{224} di Catania, Ospedale Garibaldi, 95123 Catania, Italy. ‘The systematic names and EC numbers of enzymes mentioned here are: aconitate hydratase, citrate (isocitrate) hydro-lyase, EC 4.2.1.3; alanine aminotransferase, L-alanine:2-oxoglutarate amino-transferase, EC 2.6.1.2; aspartate aminotransferase, L-aspartate:2-oxoglutarate aminotransferase, EC 2.6.1.1; ATP citrate (pro-3S)-lyase, ATP:citrate oxalacetate-lyase (pro- 3S-CH2.COO-- acetyl-CoA; ATP-dephosphorylating), EC 4.1.3.8; glucose-6-phosphat