PQQ is a growth factor and chemical attractant for a number of bacteria. Bacteria defined as acidobacteria and methylotrophic bacteria produce PQQ. Acidobacteria are common to soil and methylotrophs are organisms that can use reduced one-carbon compounds, such as methanol or methane, as the carbon source for their growth. Of potential importance to human health, PQQ is also utilized as a cofactor by bacteria that do not normally produce it as a part of their metabolism. A good example is Escherichia coli (E. coli), the gram-negative, rod-shaped bacterium that is commonly found in the intestine. When provided PQQ, E. coli utilizes it as an enzymatic cofactor in enzymes important to glucose and alcohol metabolism. Although it seems likely that PQQ supplements may alter metabolic features of E. coli, whether PQQ influences lactobacillus and other organisms that are utilized as probiotics remain to be examined. Making the link between PQQ and probiotic use nevertheless has potential in describing certain effects of PQQ.
With the above said, however, we would be remiss if we did not also note that if PQQ has the potential of influencing probiotics. One has to also ask the question of whether there is any impact on organisms, such as helicobacter pylori that have been associated with gastritis and gastric ulcers. Only one study has been done that actually examines gut microflora in the context of PQQ supplementation and its potential effects (Smidt et al., Does the intestinal microflora synthesize pyrroloquinoline quinone? Biofactors. 1991; 3:53-9). That study indicates that it is difficult to demonstrate PQQ synthesis by the microflora that is present in the gut. Using a mouse as a model, there was also little change in the amounts of organisms that were reported to present in the intestine before versus after PQQ supplementation.
PQQ supplementation may be complementary to probiotic use, but more work needs to be done. We also encourage you to read reviews that indicate the human body may respond differently to the different species and strains of probiotics (e.g., see Hakansson et al., Gut microbiota and inflammation. Nutrients. 2011; 3:637-82).
Does it make sense to call pyrroloquinoline quinone, vitamin PQQ?
To make the case for the physiological and biomedical importance of PQQ, it is also important to appreciate that many of pyrroloquinoline quinone’s biological functions are universal.
Pyrroloquinoline quinone acts as a growth factor to both plant and certain strains of bacteria. PQQ is a trophic factor important to the growth and metabolism of methylotrophic bacteria (bacteria capable of growing on simple carbon sources). Although a role as a vitamin-like cofactor has not been established in animals or plants, many bacteria utilize PQQ as an enzyme cofactor. Enzymes containing PQQ have sometimes designated quinoproteins (proteins that contain biologically active quinone components). Most of these enzymes act as dehydrogenases that modify a variety of sugars and alcohols in bacterial metabolic pathways. The PQQ-requiring quinoproteins/enzymes are distinguished because the PQQ associated with these proteins is dissociable (loosely bound).
An important class of bacteria that interacts with plants is rhizobacterium (predominant bacterium in soil). Rhizobacterium is one of several strains of bacteria that have developed pathways for synthesizing PQQ and now constitute a major environmental source. Plants cultivated with rhizobacterium have significantly increased height, flower number, fruit number, and size. This does not occur when genetically modified rhizobacteria unable to produce PQQ are added to cultures. Of importance, PQQ added directly to the plants as an external nutrient or trophic factor also causes plants to flower and grow. Hence, it appears that PQQ in plants and bacteria can function as a growth-promoting agent. Relatively small amounts of PQQ are needed to elicit given responses. That PQQ is present in a wide variety of foods (see PQQ Rich Foods) is due in large part to its function and presence in plants and fermented (bacterially derived products). Similar to other compounds that have physiological functions and applications in animals, PQQ is ubiquitous and appears utilized by a wide variety of organisms.
There have been a few of you concerned about pyrroloquinoline quinone and erectile dysfunction. We received the following question:
…positive results in animal studies (show) relative avoidance of ischemic reperfusion injury following induced stroke in lab animals. This was due, I understand, to PQQ’s ability to block nitric oxide synthesis. This begs the question; do you think PQQ can cause male erectile dysfunction since normal function depends on adequate levels of nitric oxide?
Pyrroloquinoline quinone is a redox-active nutrient that can scavenge various reactive oxygen species (ROS), such as superoxide radicals, which can act as deleterious oxidants. This is one of several aspects that make PQQ an effective anti-ischemic agent.
PQQ is unable to directly interact with nitric oxide. Research shows it doesn’t block nitric oxide synthesis, which in part addresses the concern about erectile dysfunction. Rather, pyrroloquinoline quinone’s effect on nitric oxide relates to its ability to reduce the levels of the major ROS derived from nitric oxide, a compound called peroxynitrite. Nitric oxide can react with superoxide radicals to form the product, peroxynitrite.
Peroxynitrite is an oxidant and nitrating agent that can severely damage a wide array of molecules in one’s cells, including DNA and proteins. With respect to PQQ, less peroxynitrite is formed, when the formation of superoxide is blocked or reduced, because of PQQ’s ability to act as an anti-oxidant.