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Table 2 Different types of pectic substances and pectinolytic enzymes responsible for its degradation

From: Structural and functional properties of pectin and lignin–carbohydrate complexes de-esterases: a review

S. no Different types of pectic substances
1. Protopectin: Protopectin is present in the inner tissues of plant cell walls which is insoluble in water. Upon restricted hydrolysis yields pectin or pectic acids
2. Pectic acid: Pectic acids are soluble pectic substances (galacturonans) with lesser number of methoxyl groups. Normal and pectic acid salts are called as pectates
3. Pectinic acids: Are long polygalacturonans with < 75% methylated galacturonate units, salts of pectinic acids are called pectinates
4. Pectin: (or) Polymethyl galacturonate is a polymeric material with 75% of the carboxyl groups are esterified with methanol. Pectin provides rigidity to the plant cell walls
  Pectinolytic enzymes
1. Pectin methyl esterases: These esterases catalyze the de-esterification pectin by releasing methoxy esters, resulting in pectic acids and methanol
2. Pectin-depolymerizing enzymes
(a) Protopectins are enzymatically hydrolyzed by set of enzymes called as protopectinases (PPase). PPase are classified into two types (a) A-type PPase, which reacts with polygalacturonic acid regions and (b) B-type PPase reacts with the polysaccharide chains on outer region. (Protopectin(insoluble) + H2O–(PPase)– → Pectin(soluble))
(b) The pectin-depolymerizing enzymes can be majorly classified as hydrolases divided into: Endo and Exo polygalacturonases such as (Exo-polygalacturonan-digalacturono hydrolase, Oligo galacturonate hydrolase, Delta 4:5 Unsaturated oligo galacturonate hydrolases, Endo-polymethyl-galacturonases, Endo-polymethyl-galacturonases). Lyases which majorly contains enzymes such as Endo and Exo polygalacturonase lyases