This article reports a first contribution for the elucidation of catalytic mechanism of Lipase from porcine pancreas, type VI-s (PPL), in hydrolyzing an ester substrate in aqueous media. The conclusions were based on the pH-profiles of Michaelis-Menten parameters k cat /K m , k cat and K m , as well as on the absolute temperature profile of k cat /K m , obtained during the hydrolysis of p-nitrophenyl laurate by PPL. It was found that (a) PPL performs catalysis by means of ion pairs formed

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... as Ser 152 -Ο -/His 263 -Im + H and/or Carbonyl-Ο -/His 263 -Im + H, (b) the parameter k cat /K m equals to k 1 and thus ES is formed and destroyed in the course of a series of consecutive reactions governed by the dynamic constant K S = k 2 /k 1 , and (c) the hydrolysis of substrate is assisted by a hydrogen bond developed between deprotonated Asp 176 and the positively charged imidazole of His 263 across a pK a -value 3.85, necessary for efficient catalysis.