PMID: 11337010May 5, 2001Paper

Enzyme activities in the light of the membrane hypothesis of aging. [An answer to K. Kitani, Mech. Ageing Dev. 107 (1999), 299-322

Mechanisms of Ageing and Development
I Zs-Nagy

Abstract

The paper of Kitani cited in the title has raised an apparent contradiction regarding the validity of certain aspects of the membrane hypothesis of aging (MHA). He collected data showing that a number of detoxifying liver enzyme activities, although decline with age in male Fischer 344 rats, remain at an unchanged level in females of the same strain. He concluded that the main assumption of the MHA, according to which intracellular enzyme activities generally decline with age, cannot be maintained, and invoked me (p. 312) 'ellipsis to provide in the future ample (and convincing) evidence' in this respect. The present paper answers this criticism by showing that the apparent contradiction mentioned above is based on a misunderstanding on behalf of Kitani. Namely, MHA speaks about the general, density-dependent decline of the catalytic rate constant of any enzyme (k(cat)), i.e., activity per mole of enzyme, being the true specific activity of the enzymes. This parameter inevitably decreases at the increased physical density of the intracellular colloids during aging. This statement derives from the molecular enzyme kinetic models, and has extensively been proven experimentally, too. On the other hand, Kitani speaks about enzyme a...Continue Reading

Citations

Jun 13, 2009·Nihon Ronen Igakkai zasshi. Japanese journal of geriatrics·Sataro Goto

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