enzymes in the environment

enzymes are the catalysts of life. they are the link between higher forms of biological structure- cells, organisms, ecosystems- and the physical universe. they form such links by allowing incredible reactions to occur, reactions that strip complex molecules down into simple components that our cells can harvest energy from, reactions that detoxify harmful substances, reactions that take nonliving compounds and turn them into something organic. they have ugly names. ribulose-1,5-bisphosphate carboxylase oxygenase is a name that most eyes would glaze over while reading, but what if i told you that RuBisCO (it has a nickname!) is the only thing on earth that can add electrons to carbon dioxide? if that doesn’t seem to impressive, look out your window. not a single tree, flower, blade of grass, animal or human being (or man-made structure, for that matter) would exist if RuBisCO had not evolved to turn carbon dioxide into sugars.

there is a less appreciated truth about enzymes that i find to be equally intriguing, almost poetic. enzymes not only build and maintain life, they destroy it. or, to be a bit more accurate, they recycle its components. enzymes are largely responsible for decomposing organic matter, breaking down trees and blades of grass and human beings into the tiny carbon-rich compounds that RuBisCO created. in fact, if you take a small handful of soil from your garden, you are holding billions of free floating enzymes. they have been constructed by plants and microbes and were released into the environment to acquire something that their creator needs (i hate to use the word “creator”, when writing about science, if you have a better word, please do share). most often, this is an essential nutrient or a small sugar that can be used for energy. imagine if you could take your stomach out, and send it off to wendy’s to eat a chicken sandwich for you. not the prettiest analogy, perhaps, but this is in essence this is what microbes and plants do in the soil.

while intellectually it may be somewhat interesting to imagine billions of microbial exo-stomachs scouring the earth for their lunch, why should anyone really care about enzymes in the environment? well, truth be told, very few people do. but i’m going to tell you why an increasing number of environmental scientists are taking an interest in enzymes, not only in order to understand a process, but with the growing realization that understanding how enzymes shape our planet may be essential to averting looming environmental catastrophes.

as the agents responsible for the breakdown of organic, carbon containing compounds (and this is true in soils and aquatic ecosystems), enzymes are gatekeepers. they regulate how quickly carbon is broken down and taken up anew by living organisms. if you want to think realistically about any form of carbon sequestration in soils (an idea that has exploded in popularity in the last several years), or understand how global warming is altering ecosystems and the balance of carbon and nutrients within them, you simply cannot ignore enzymes.

the fact is, much as we would like to find a way to store the huge amounts of  carbon our activities are releasing into the atmosphere back in the earth, adding carbon feeds the soil. and just as human populations increase during times of food surplus, microbial populations explode, produce more enzymes and cycle that carbon at a faster rate.

another aspect of enzyme behavior that makes global climate change scenarios even stickier is that enzymes are very, very sensitive to changes in their environment. the activity and efficiency of enzymes in the environment is closely linked to temperature, moisture, and pH conditions. my own research on soil enzymes from northeastern forests is showing that even a few degrees of temperature increase can cause a dramatic increase in the rate of the carbon-cycling reactions that these enzymes perform. droughts, on the other hand, can quickly kill demolish enzyme communities and cause carbon cycling in a system to drop off.

the behavior of enzymes in the environment, we are discovering, is far more complex and nuanced than the story i’ve outlined here. moreover, ecologists know that enzymes must be understood within a broad context. the plants, animals and environmental processes that interact to form complex ecosystems, which enzymes regulate on a very fundamental level, must be somehow integrated if we are to fully understand how these tiny reaction machines keep our earth running.

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