In the presence of taurodeoxycholate, cis-unsaturated fatty acids increase porcine pancreatic lipase activity 15-fold at pH 7.5. When the substrate is emulsified by taurodeoxycholate, the pH optimum for lipase ranges from 6.2 to 7.0. In the presence of cis-unsaturated fatty acids, the overall activity of lipase increases, the pH optimum shifts, and the pH-activity curve becomes biphasic, with one optimum around pH 7.7 and the other around pH 8.8.

Pancreatic lipases are interfacial enzymes whose adsorption to the lipid-water interface is essential for catalysis. The study compares lipid binding properties across species and shows that the interaction with the interface is sensitive to enzyme-specific properties that influence adsorption and catalytic performance. These findings support the idea that changes in binding can alter lipase efficiency on fats.

Several hypotheses can be raised to explain this low activity. First of all, the protonation state of the active site may not be appropriate, disturbing the electrostatic interactions essential for catalysis. The environmental pH may also influence the lid dynamics since key residues are involved in electrostatic interactions stabilizing the open conformation. In an acidic environment, the lid moved toward a close conformation while a neutral environment was more favorable to an open conformation.

The open and closed states and their protonation states are observed in the crystal structure at 0.91 Å resolution. The findings indicate a role for Asp145 and Lys290 in the conformational change. The analysis shows that protonation of charged residues can alter lipase conformation and that the charge inside the cavity is conserved even as individual residues change protonation state.

Cystic fibrosis is associated with pancreatic insufficiency and acidic intraluminal conditions that limit the action of pancreatic enzyme replacement therapy, especially that of lipase. In vitro, pancreatic lipase exhibits the maximum activity at pH 7.5–8.5, whereas in cystic fibrosis the low intestinal pH greatly impairs its activity. The very low activity of pancreatic lipase at acidic pH can only be partly explained by pH-induced conformational changes since HuPL retained about 50% of its activity after 1 h incubation at pH 5 in the presence of all lipolysis partners.

Like most lipases, human pancreatic lipase (HPL) displays a catalytic triad and an oxyanion hole that are built from the highly conserved amino acids Ser152, His263, Asp176 and residues Gly77, His151, respectively. In solution, HPL adopts a closed conformation in which a surface loop, the lid (residues 238–262), folds over the active site and prevents substrate access. Interfacial activation is linked to pH and lipid interface; changes in protonation of charged residues at the interface or in the lid region are thought to modulate the equilibrium between closed and open conformations, thereby affecting catalytic efficiency.

Access to the active site of pancreatic lipase is controlled by a surface loop, the lid, which normally undergoes conformational changes only upon addition of lipids or amphiphiles. These differences among PLRP2s might be explained by differences in the amino acid residues that are involved in the stabilization of the lid conformations. The article directly links lid conformation to residues that stabilize open and closed states.

These results demonstrate that Ser153 is involved in the catalytic site of pancreatic lipase and is not crucial for interfacial binding. The paper experimentally distinguishes catalytic-site residues from residues involved in interfacial binding, which is relevant to claims about pH-driven changes affecting binding versus catalysis.

The adsorption of pancreatic lipase to the lipid-water interface is pH-dependent, and acidic conditions reduce its interfacial binding. The study links protonation state changes at specific amino acid residues to altered adsorption behavior, which in turn affects enzymatic activity on triglyceride substrates.

Pancreatic lipase and its zymogen were studied as a function of pH by circular dichroism and fluorescence spectroscopy. A reversible conformational transition was observed between pH 6 and 8, associated with changes in the environment of aromatic residues. This transition correlated with a marked change in enzymatic activity, indicating that protonation–deprotonation of specific amino acid side chains induces small structural rearrangements that modulate the active site accessibility and catalytic efficiency.

Human pancreatic lipase is optimally active in the physiological pH range of the duodenum (around pH 7–8). At lower pH values its activity decreases sharply. This behavior is related to ionization of amino acid residues at the catalytic site and at the lipid–water interface, which affects the enzyme–substrate binding and interfacial activation. Protonation of charged residues modifies electrostatic interactions and can slightly change the shape or dynamics of the active site, resulting in reduced affinity for lipid substrates.

Pancreatic lipase activity is affected by intestinal pH, the presence of colipase and bile salts. Pancreatic lipase appears to lose catalytic activity below pH 5. The review states that low intestinal pH can leave lipase catalytically inactive and describes a sequence of conformational steps involving opening of the lid and substrate binding.

The most striking feature of this conformational change is the movement of the lid consisting of 23 amino acid residues (C237–C261), which covers the active site. The study identifies a defined lid region whose movement controls exposure of the active site, supporting the idea that structural changes can alter substrate access.

In the presence of lipase inhibitors, it undergoes conformational changes, then the solvents in the 3D structure of several lipases can be exposed to the active sites. The review discusses pancreatic lipase family structure and shows that conformational rearrangements can expose the active site to substrate or inhibitors.

Interfacial activation of lipases is strongly pH-dependent. Protonation of acidic and basic residues at the interface and within the lid and active site regions alters electrostatic interactions that stabilize the open form of the enzyme. As pH decreases below the optimum, the accumulation of additional protons on these residues leads to a shift towards less active conformations, with reduced affinity of the enzyme for lipid substrates at the interface.

The chapter notes that “every enzyme also has an optimum pH at which it works best,” and lists “Lipase (pancreas) – 8.0” in a table of optimal pH values. It explains mechanistically how changing pH alters residue protonation and charge: at lower pH, “the –COO− will pick up a hydrogen ion… You no longer have the ability to form ionic bonds between the substrate and the enzyme. If those bonds were necessary to attach the substrate and activate it… then at this lower pH, the enzyme won’t work.” At higher pH, “the –NH3+ group will lose a hydrogen ion… Again, there is no possibility of forming ionic bonds.” The text adds that changes in rate as pH shifts from optimum can be viewed as “inhibition by hydrogen ions” on the acidic side and by hydroxide on the basic side, reflecting altered protonation of catalytic or binding groups.

In describing the pH dependence of various lipases, the authors write: “RGL and rDGL are known to display an optimal activity at an acidic pH… rHPL and PPL prefer to catalyze the hydrolysis of TG at neutral or slightly alkaline pH.” The assay they describe measures lipase activity over pH 5.0–9.2 and relies on changes in protonation: “The lipase activity measurement is based on the decrease of the pH indicator optical density due to protonation which is caused by the release of FFAs during the hydrolysis of TGs and thus acidification.” This illustrates that lipase catalytic function is strongly modulated by environmental pH, which affects protonation equilibria tied to catalysis and substrate interaction.

Lipases exhibit a characteristic bell-shaped pH–activity profile, with maximum activity near their physiological pH. Deviations toward acidic pH often cause protonation of surface and active-site residues, thereby altering hydrogen bonding and salt bridges that maintain the open, active conformation. These changes are usually subtle and reversible, but they lower catalytic efficiency by decreasing substrate binding or the rate of acyl-enzyme formation.

Pancreatic lipase attaches to the surface of triglyceride globules. In the right conditions, pancreatic lipase is very efficient. Right conditions include neutral pH, mixing, bile salts, and co-lipase. The material also notes that pancreatic lipase has pH optima in the acidic-to-neutral range for some contexts, but is presented as working most efficiently under neutral milieu with bile salts and co-lipase.

This structural review notes that “Pancreatic lipase is critical for the digestion and absorption of dietary fats… The enzymatic mechanism of lipase is similar to that of serine hydrolases and centered on the active site serine.” It describes that the catalytic machinery (Ser-His-Asp triad) and the surrounding ‘lid’ region control substrate access and interfacial activation, and that electrostatic interactions in this region are important for stabilizing the open, active conformation. While not focused on pH, the paper underlines how modest changes in the electrostatic environment around active site residues and the lid can influence binding and catalysis.

This study states that “For a lipase to catalyze a reaction, the enzyme–substrate complex must be stable, and the active site residues must be in an optimal arrangement for catalysis.” Using simulations and experiments in non-aqueous media, it finds that “the stability and conformation of the active site pocket are important factors influencing the performance of the lipases.” While the focus is on organic solvents and water activity rather than pH, the work supports the general principle that subtle changes in local environment that affect active-site residue protonation and hydrogen bonding can alter active-site geometry and catalytic efficiency.

Enzyme activity is strongly influenced by pH because amino acid residues in the active site and substrate-binding regions can gain or lose protons. When the environmental pH becomes more acidic, certain residues become protonated, which changes their charge. Such changes can alter the shape or electrostatic properties of the active site, typically reducing the binding affinity for substrates and lowering catalytic efficiency when the pH moves away from the enzyme’s optimum.

Although this paper is about gastric lipase rather than pancreatic lipase, it provides mechanistic context for interfacial lipases: pH-dependent adsorption to hydrophobic surfaces was shown to be reversible and optimum at low pH, indicating that protonation state can alter enzyme adsorption and apparent activity at lipid-water interfaces.

The overview notes that pancreatic lipase “is most active at neutral to slightly alkaline pH” and functions in the duodenum in conjunction with colipase and bile salts. It contrasts this with gastric lipase, which has an acidic pH optimum. The article emphasizes that pancreatic lipase activity falls sharply outside its optimal pH range and that its conformation and interaction with colipase and lipid interfaces depend on the physicochemical environment, including pH.

StatPearls describes lipases as enzymes that “break down triglycerides into free fatty acids and glycerol by catalyzing the hydrolysis of the ester bonds in triglycerides.” It explains that different lipases have different pH optima depending on their physiological environment, with pancreatic lipase acting in the small intestine and gastric lipase in the stomach. The article notes that alterations in pH from normal physiological values can impair lipase function, reflecting the dependence of catalytic activity on proper enzyme conformation and ionization states.

This article notes that human pancreatic lipase is the main enzyme in the digestive system that degrades dietary triacylglycerol to monoacylglycerol and fatty acids and that it operates in the small intestine where the pH is close to neutral to slightly alkaline. It explains that like other enzymes, lipases have an optimal pH range and that their activity decreases when the pH deviates from this optimum, because the ionization state of amino acid residues in the active site and at the interface is altered.

The guide states that lipases generally have an optimal pH range of about 4.0–8.0 and that under extreme pH conditions they can lose activity or denature. It further notes that modifications of structural features can enhance pH tolerance, implicitly acknowledging that changes in protonation and charge distribution at different pH values influence the structure and activity of lipases.

Human pancreatic lipase (PNLIP) is a classic serine hydrolase whose activity depends on lid opening and interfacial activation. Acidic conditions can reduce activity by changing protonation states of ionizable residues and weakening interactions that stabilize the open conformation, but the exact residues and magnitude of effect depend on the enzyme construct and experimental conditions.