Dear Shwethashree Malla,

Please read the following text:

Exoenzymes:

In eukaryotic cells, exoenzymes are manufactured like any other enzyme via protein synthesis, and are transported via the secretory pathway. After moving through the rough endoplasmic reticulum, they are processed through the Golgi apparatus, where they are packaged in vesicles and released out of the cell. In humans, a majority of such exoenzymes can be found in the digestive system and are used for metabolic breakdown of macronutrients via hydrolysis. Breakdown of these nutrients allows for their incorporation into other metabolic pathways.

Endoenzyme:

An endoenzyme, or intracellular enzyme, is an enzyme that functions within the cell in which it was produced. Because the majority of enzymes fall within this category, the term is used primarily to differentiate a specific enzyme from an exoenzyme. It is possible for a single enzyme to have both endoenzymatic and exoenzymatic functions.

Example:Glycolytic enzymes,enzymes of Kreb's Cycle. enzymes are a type of protein that speed up chemical reactions in cells. enzymes are specific to the job they do. only molecules that are the correct shape can fit into the enzyme. this is called the lock and key model. enzymes work outside of the cell (extracellular enzymes) as well as inside the cell (intracellular enzymes) In most cases the term endoenzyme refers to an enzyme that binds to a bond 'within the body' of a large molecule - usually a polymer. For example an endoamylase would break down large amylose molecules into shorter dextrin chains. On the other hand, an exoenzyme removes subunits from the polymer one at a time from one end; in effect it can only act at the end ponts of a polymer. An exoamylase would therefore remove one glucose molecule at a time from the end of an amylose molecule.

Exo (extra) vs. Endo (intra)

intra (meaning --within) cellular enzymes are the common metabolic enzymes that are responsible for catalyzing all those processes we need in our cells---relaese of energy from glucose or carbohydrates, lipids, proteins------- replication of DNA----synthesis of proteins and hundreds of others------(a really cool one is---- acetylcholinesterase--check it out)

extra (meaning outside) cellular enzymes are released by the cells after being packaged by the golgi body or released straight out the membrane to perform a job external to that cell (ie digestive enzymes of our own digestive system--salivary, peptic and pancreatic enzymes to name some general types).

Lodish, Harvey (2008). Molecular cell biology (6th ed., [2nd print.]. ed.). New York Freeman. ISBN 0716776014.

Andrews, Lary. "Supplemental Enzymes for Digestion". Health and Healing Research. Retrieved 9 December 2013.

Hoping this will be helpful,

Rafik

Bacteria have dedicated systems for protein secretion. Here is a review article of the systems in Gram negative bacteria.

http://jb.asm.org/content/187/13/4306

Dear Adam,

I have read your attached review and found that there is no indication of how exoenzymes transport from the inside to outside the cell.

I have copied the part of the conclusion relates to this issue:

"Many more questions still remain to be addressed regarding protein export across the bacterial OM. What is the folding state of the secreted proteins before and during their transport across the OM? How are unfolded or partially folded proteins protected against proteolytic degradation? How do secreted proteins and macromolecular secretion machines get through the peptidoglycan layer? If energy sources are not present in the periplasm and the OM, how do molecules as large as the secreted proteins overcome the unfavorable entropy constraints and pass through the hydrophobic membrane environment? Are any chaperones universally required? What is the fate of an OM transporter after secretion? How do the OM pores prevent leakage of small periplasmic molecules? What mechanisms are involved in channel gating? How is specificity of secreted proteins assured in general? What is the architecture of the T4S and T3S machineries? What are the structures of the components of the different secretion apparatuses? Answers to these questions will provide a more complete picture of the secretion process and will lead to more efficient means of protection against bacterial infections".

For your consideration,

Rafik

Thank you very much Rafik Sir and Adam Sir.

The explanations were indeed helpful.