Extracellular digestion

Phagocytosis is an important mechanism for the organism to rid itself of bacteria and pathogenic material, as well as cell debris and remnants of apoptosis. However, it can also provide a route for the uptake of pollutant particulate material. It is seen to be especially important in the incorporation of airborne particulate material, which often has serious health consequences (see Section 6.4). In terrestrial invertebrates, food is obtained either from particulate matter in the soil or from molecules dissolved in interstitial water. Most of these organisms have extracellular digestion, with nutrients and foreign material being absorbed by one or more of the routes available for transport across membranes, such as diffusion, channels or pinocytosis. There have been few studies to establish which route is taken. 

Extracellular digestion (GI tract) Intracellular digestion (lysosomes) Modification for food use... 

Lysosomes function in intracellular and extracellular digestion. They are capable of degrading most biomolecules. Lysosomes participate in the life of a cell in three fundamental ways (1) digestion of food molecules or other substances taken into the cell by endocytosis (a process illustrated in Figure 2.22), (2) digestion of worn out or unnecessary cell components, and (3) breakdown of extracellular material. 

The function of lysosomes is intracellular and extracellular digestion. These spherical, membranous organelles contain a group of enzymes called acid hydrolases, which degrade most biomolecules. 

Lysosomes are saclike organelles that function in intracellular and extracellular digestion. They contain digestive enzymes that can degrade most biomolecules. 

Mean serum baseline free MMP-1 was reported to be decreased 25% and baseline free TIMP-1 was increased 50% in hypertensives compared with normotensive patients. Hypertensive patients with baseline left ventricular hypertrophy exhibited lower levels of free MMP-1 and carboxyl terminal telopeptide of collagen type I and higher values of free TIMP-1 than did hypertensive patients without baseline left ventricular hypertrophy. Laviades (LI) suggested that extracellular digestion of collagen type I is depressed in essential hypertension and may facilitate organ fibrosis in hypertensive individuals. 

Proteolytic enzymes were originally studied as extracellular digestive enzymes, and the first sources studied were the stomach and pancreas. Later intracellular proteolytic enzymes from nondigestive oi ans were studied. The intracellular proteolytic enzymes from all cells are called cathepsins. The isolation of cathepsins has not been so successful as the isolation of digestive enzymes because of their lower concentrations and greater labilities. In addition to animal sources, both plants and microorganisms have been studied as sources of proteolytic enzymes. Enzymes from these various sources show many different properties. Some of these will be discussed in connection with individual enzymes. 

Extracellular digestion compared to intracellular digestion implies that specialization has occurred in the sense of a relatively great biosynthesis of enzymes secreted into the lumen of the digestive tube and constantly renewed. Intracellular digestion is the primitive form. It is the only form of digestion in the Spongiae. 

As Yonge has emphasized, an example that demonstrates very well the relation between the system of intracellular digestion and that of extracellular digestion is the Molluscs among them we find all stages between an almost complete intracellular digestion and a totally extracellular... 

This introduction serves as prima facia evidence for probability of extracellular chitinase(s)operating in complex marine systems. The pure crystalline chitin of diatoms and the complexed chitin of arthropod exoskeletons and other animals are available for extracellular digestion by organisms diverse as bacteria, oysters, and fish, but yet there is no report of extant extracellular chitinase in water or in sediment. The only existing report this author is aware of, regarding extant chitinase environmental activities is relative to the arctic soil mycorhizzosphere (Linkins and Neal, 1982). 

Chitinase induction in estuarine sediments was documented. Although the polymer chitin (poly-N-acetyl-D-glucosamine) is the major organic component of all arthropod exoskeletons and is prolific in the diatoms, there has been no demonstration of the chit in-induced hydrolytic enzymes (chitinases) responsible for the extracellular digestion of these ubiquitous chitins. Blue crab (Callinectes sapidus) exoskeleton was dosed into compacted anaerobic muds. Subsequent incubation for 30 d under aerobic ambient seawater conditions (28° C 12-15 ppt salinity) resulted in significant increases of chitinase in amended sediment as compared to controls which had... 

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