Important Digestive Enzymes of Earthworm

Abstract

The living cell is the site of tremendous biochemical activity called metabolism. This is the process of chemical and physical change which goes on continually in the living organism. The greatest majority of these biochemical reactions do not take place spontaneously (Bennett and Frieden. Modern topics in biochemistry. Macmillan, London, pp 43–45, 1969). The phenomenon of catalysis makes possible biochemical reactions necessary for all life processes. The catalysts of biochemical reactions are enzymes and are responsible for bringing about almost all of the chemical reactions in living organisms (Holum. Elements of general and biological chemistry, 2nd edn. Wiley, New York, p 377, 1968). Without enzymes, these reactions take place at a rate far too slow for the pace of metabolism (Martinek. J Am Med Tech 31:162, 1969). All known enzymes are proteins. They are high molecular weight compounds made up principally of chains of amino acids linked together by peptide bonds (Pfeiffer. Enzymes, the physics and chemistry of life. Simon and Schuster, New York, pp 171–173, 1954). A protein molecule consists of one or more polypeptide chains which continue without interruption throughout the molecule folded into a uniquely defined configuration held together by hydrogen bonds between the peptide nitrogen and oxygen atoms also between the charged sidechains (Blow. Structure 8(4):R77–R81, 2000). It has long been assumed that most invertebrates do not possess the enzymatic complement to digest polysaccharides, but now the opposite is often shown for different groups of soil fauna, enabling us redefine species diets and therefore their ecological function. Enzymatic activities have been widely used as an index of soil fertility or ecosystem status because they are involved in biological transformation of native and foreign compounds in soils (Tate. Soil microbiology, 2nd edn. Wiley, New York, 2000). The digestive enzymes of the litter feeding animals, particularly oligochaetes, are responsible for decomposition and humification processes (Parthasarathi and Ranganathan. Trop Ecol 41(2):251–254, 2000). The interpretation of data arising from enzyme assay is complicated since enzyme activity depends on several factors and different locations of enzymes in the studied system (Nannipieri et al. Enzyme activities and microbiological and biochemical processes in soil. In: Burns RG, Dick R (eds) Enzymes in the environment. Marcel Dekker, New York, pp 1–33, 2002). So far only a few enzymatic studies on earthworm casts have been published, and they are limited to observations on soil only (Parthasarathi and Ranganathan. Trop Ecol 41(2):251–254, 2000). Some authors have described a direct role of earthworms in the decomposition of plant debris, and presume the existence of their own digestive enzymatic activities. Worms being hermaphrodites with simultaneous functioning gonads may require more energy and increased enzyme activities during this active phase of reproduction. Enzyme activity is influenced also by type of food. The differential enzyme-activity is perhaps related to the type of food and rate of eating of each species (Table 5.1). Earthworm which feed and depend on microbes, litter, and grit present in soil should contain battery of enzymes. Earthworm castings are known to be a rich source of plant growth promoting substances viz., growth hormones, enzymes and vitamins (Karthikeyan et al. AgroIndia 7:34–353, 2004). Earthworm castings also contains a number of beneficial microorganisms, nitrogen fixing, phosphorous solubilizing and cellulose decomposing organisms, which help in improving soil productivity. Earthworms have an in-house supply of enzymes like Nitrate reductase, acid phosphatase and alkaline phosphatase, which are involved in the metabolism of nitrogen and phosphate materials present in the compost. The earthworms speed up the composting process and transform wastes into nutrient rich castings with the help of the enzymes (Prabha et al. South Asian J Socio-Polit Stud 2:129–130–156, 2005).