The inhibition effect of cellobiose on the initial stage of hydrolysis when cellobiohydrolase Cel 7A and endoglucanases Cel 7B, Cel 5A, and Cel 12A from Trichoderma reesei were acting on bacterial cellulose and amorphous cellulose that were [(3)H]- labeled at the reducing end was quantified. The apparent competitive inhibition constant (K(i)) for Cel 7A on [(3)H]-bacterial cellulose was found to be 1.6 +/- 0.5 mM, 100-fold higher than that for Cel 7A acting on low-molecular-weight model substrates. The hydrolysis of [(3)H]-amorphous cellulose by endoglucanases was even less affected by cellobiose inhibition with apparent K(i) values of 11 +/- 3 mM and 34 +/- 6 mM for Cel 7B and Cel 5A, respectively. Contrary to the case for the other enzymes studied, the release of radioactive label by Cel 12A was stimulated by cellobiose, possibly due to a more pronounced transglycosylating activity. Theoretical analysis of the inhibition of Cel 7A by cellobiose predicted an inhibition analogous to that of mixed type with two limiting cases, competitive inhibition if the prevalent enzyme-substrate complex without inhibitor is productive and conventional mixed type when the prevalent enzyme-substrate complex is nonproductive.

Mitochondrial dysfunction is a hallmark of almost all diseases. Acquired or inherited mutations of the mitochondrial genome DNA may give rise to mitochondrial diseases. Another class of disorders, in which mitochondrial impairments are initiated by extramitochondrial factors, includes neurodegenerative diseases and syndromes resulting OPEN ACCESSInt. J. Mol. Sci. 2009, 10 2253 from typical pathological processes, such as hypoxia/ischemia, inflammation, intoxications, and carcinogenesis. Both classes of diseases lead to cellular energetic depression (CED), which is characterized by decreased cytosolic phosphorylation potential that suppresses the cell's ability to do work and control the intracellular Ca 2+ homeostasis and its redox state. If progressing, CED leads to cell death, whose type is linked to the functional status of the mitochondria. In the case of limited deterioration, when some amounts of ATP can still be generated due to oxidative phosphorylation (OXPHOS), mitochondria launch the apoptotic cell death program by release of cytochrome c. Following pronounced CED, cytoplasmic ATP levels fall below the thresholds required for processing the ATP-dependent apoptotic cascade and the cell dies from necrosis. Both types of death can be grouped together as a mitochondrial cell death (MCD). However, there exist multiple adaptive reactions aimed at protecting cells against CED. In this context, a metabolic shift characterized by suppression of OXPHOS combined with activation of aerobic glycolysis as the main pathway for ATP synthesis (Warburg effect) is of central importance. Whereas this type of adaptation is sufficiently effective to avoid CED and to control the cellular redox state, thereby ensuring the cell survival, it also favors the avoidance of apoptotic cell death. This scenario may underlie uncontrolled cellular proliferation and growth, eventually resulting in carcinogenesis.

Expression and function of creatine kinase (CK), adenylate kinase (AK) and hexokinase (HK) isoforms in relation to their roles in regulation of oxidative phosphorylation (OXPHOS) and intracellular energy transfer were assessed in beating (B) and non-beating (NB) cardiac HL-l cell lines and adult rat cardiomyocytes or myocardium. In both types of HL-1 cells, the AK2, CKB, HK1 and HK2 genes were expressed at higher levels than the CKM, CKMT2 and AK1 genes. Contrary to the saponin-permeabilized cardiomyocytes the OXPHOS was coupled to mitochondrial AK and HK but not to mitochondrial CK, and neither direct transfer of adenine nucleotides between CaMgATPases and mitochondria nor functional coupling between CK-MM and CaMgATPases was observed in permeabilized HL-1 cells. The HL-1 cells also exhibited deficient complex I of the respiratory chain. In conclusion, contrary to cardiomyocytes where mitochondria and CaMgATPases are organized into tight complexes which ensure effective energy transfer and feedback signaling between these structures via specialized pathways mediated by CK and AK isoforms and direct adenine nucleotide channeling, these complexes do not exist in HL-1 cells due to less organized energy metabolism.

Corpus dominant atrophic gastritis is characterized by decreased respiratory capacity and relative deficiency of the respiratory complex I of mitochondria in the mucosa, the latter defect probably limiting mitochondrial ATP production and energetic support of the secretory function of the zymogenic mucosal cells.