diff --git a/docs/enzymes.rst b/docs/enzymes.rst
index 6635b6ab66160232666a02fbdf36b246b3533cf3..513e8637de4dfb4ce0fe93dd29feebdfa929c99d 100644
--- a/docs/enzymes.rst
+++ b/docs/enzymes.rst
@@ -7,6 +7,10 @@ All default available enzymes (`enzymes_definition.py`) are listed bellow.
 
 For each of them, there is the equivalent in `RPG` grammar.
 
+On the following, nomenclature of `Schechter and Berger <https://www.ncbi.nlm.nih.gov/pubmed/6035483>`_ is used. According to it, amino acids before the cleavage site are designated as `P1`, `P2`, `P3`, etc in the N-terminal direction, and as `P1'`, `P2'`, `P3'`, etc in the C-terminal direction. For example, with cleavage site represented as '|'::
+
+    ...P3-P2-P1-|-P1'-P2'-P3'...
+
 -----------------
 Available enzymes
 -----------------
@@ -29,7 +33,7 @@ Available enzymes
 Arg-C
 .....
 
-Arg-C proteinase proteinase preferentially cleaves after R
+Arg-C proteinase proteinase preferentially cleaves after R (`P1`)
 
 **RPG definition:**
 
@@ -47,7 +51,7 @@ https://web.expasy.org/peptide_cutter/peptidecutter_enzymes.html#ArgC
 Asp-N
 .....
 
-Asp-N Sequencing Grade preferentially cleaves before C or D
+Asp-N Sequencing Grade preferentially cleaves before C or D (`P1'`)
 
 **RPG definition:**
 
@@ -65,7 +69,7 @@ https://france.promega.com/resources/pubhub/using-endoproteinases-asp-n-and-glu-
 BNPS-Skatole
 ............
 
-BNPS-Skatole preferentially cleaves after W
+BNPS-Skatole preferentially cleaves after W (`P1`)
 
 **RPG definition:**
 
@@ -83,7 +87,7 @@ https://web.expasy.org/peptide_cutter/peptidecutter_enzymes.html#BNPS
 Caspase 1
 .........
 
-Caspase 1 preferentially cleaves after D preceded by H, A or T in `P2` and preceded by F, W, Y or L in `P4`. It will not cleave if D is followed by P, E, D, Q ,K or R
+Caspase 1 preferentially cleaves after D (`P1`) preceded by H, A or T in `P2` and preceded by F, W, Y or L in `P4`. It will not cleave if D is followed by P, E, D, Q ,K or R in `P1'`.
 
 **RPG definition:**
 
@@ -105,7 +109,7 @@ https://web.expasy.org/peptide_cutter/peptidecutter_enzymes.html#Casp1
 Caspase 2
 .........
 
-Caspase 2 preferentially cleaves after D preceded by DVA or DEH. It will not cleave if D is followed by P, E, D, Q ,K or R. 
+Caspase 2 preferentially cleaves after D (`P1`) preceded by DVA or DEH. It will not cleave if D is followed by P, E, D, Q ,K or R in `P1'`. 
 
 **RPG definition:**
 
@@ -129,7 +133,7 @@ https://web.expasy.org/peptide_cutter/peptidecutter_enzymes.html#Casp2
 Caspase 3
 .........
 
-Caspase 3 preferentially cleaves after D preceded by DMQ or DEV. It will not cleave if D is followed by P, E, D, Q ,K or R. 
+Caspase 3 preferentially cleaves after D (`P1`) preceded by DMQ or DEV. It will not cleave if D is followed by P, E, D, Q ,K or R in `P1'`. 
 
 **RPG definition:**
 
@@ -153,7 +157,7 @@ https://web.expasy.org/peptide_cutter/peptidecutter_enzymes.html#Casp3
 Caspase 4
 .........
 
-Caspase 4 preferentially cleaves after D preceded by LEV or (W/L)EH. It will not cleave if D is followed by P, E, D, Q ,K or R. 
+Caspase 4 preferentially cleaves after D (`P1`) preceded by LEV or (W/L)EH. It will not cleave if D is followed by P, E, D, Q ,K or R in `P1'`. 
 
 **RPG definition:**
 
@@ -177,7 +181,7 @@ https://web.expasy.org/peptide_cutter/peptidecutter_enzymes.html#Casp4
 Caspase 5
 .........
 
-Caspase 5 preferentially cleaves after D preceded by (W/L)EH.
+Caspase 5 preferentially cleaves after D (`P1`) preceded by (W/L)EH.
 
 **RPG definition:**
 
@@ -195,7 +199,7 @@ https://web.expasy.org/peptide_cutter/peptidecutter_enzymes.html#Casp5
 Caspase 6
 .........
 
-Caspase 6 preferentially cleaves after D preceded by VEI or VEH. It will not cleave if D is followed by P, E, D, Q ,K or R. 
+Caspase 6 preferentially cleaves after D (`P1`) preceded by VEI or VEH. It will not cleave if D is followed by P, E, D, Q ,K or R in `P1'`. 
 
 **RPG definition:**
 
@@ -217,7 +221,7 @@ https://web.expasy.org/peptide_cutter/peptidecutter_enzymes.html#Casp6
 Caspase 7
 .........
 
-Caspase 7 preferentially cleaves after D preceded by DEV. It will not cleave if D is followed by P, E, D, Q ,K or R. 
+Caspase 7 preferentially cleaves after D (`P1`) preceded by DEV. It will not cleave if D is followed by P, E, D, Q ,K or R in `P1'`. 
 
 **RPG definition:**
 
@@ -239,7 +243,7 @@ https://web.expasy.org/peptide_cutter/peptidecutter_enzymes.html#Casp7
 Caspase 8
 .........
 
-Caspase 8 preferentially cleaves after D preceded by (I/L)ET. It will not cleave if D is followed by P, E, D, Q ,K or R. 
+Caspase 8 preferentially cleaves after D (`P1`) preceded by (I/L)ET. It will not cleave if D is followed by P, E, D, Q ,K or R in `P1'`. 
 
 **RPG definition:**
 
@@ -261,7 +265,7 @@ https://web.expasy.org/peptide_cutter/peptidecutter_enzymes.html#Casp8
 Caspase 9
 .........
 
-Caspase 9 preferentially cleaves after D preceded by LEH.
+Caspase 9 preferentially cleaves after D (`P1`) preceded by LEH.
 
 **RPG definition:**
 
@@ -279,7 +283,7 @@ https://web.expasy.org/peptide_cutter/peptidecutter_enzymes.html#Casp9
 Caspase 10
 ..........
 
-Caspase 10 preferentially cleaves after D preceded by IEA.
+Caspase 10 preferentially cleaves after D (`P1`) preceded by IEA.
 
 **RPG definition:**
 
@@ -297,7 +301,7 @@ https://web.expasy.org/peptide_cutter/peptidecutter_enzymes.html#Casp10
 Chymotrypsin high specificity
 .............................
 
-This chymotrypsin preferentially cleaves after F, Y or W if not followed by P. It will not cleave after W followed by M.
+This chymotrypsin preferentially cleaves after F, Y or W (`P1`) if not followed by P in `P1'`. It will not cleave after W followed by M in `P1'`.
 
 **RPG definition:**
 
@@ -320,7 +324,7 @@ https://web.expasy.org/peptide_cutter/peptidecutter_enzymes.html#Chym
 Chymotrypsin low specificity
 .............................
 
-This chymotrypsin preferentially cleaves after F, L, Y, W, M or H if not followed by P. It will not cleave after W followed by M. It will not cleave after M followed by Y. It will not cleave after H followed by D/M/W.
+This chymotrypsin preferentially cleaves after F, L, Y, W, M or H (`P1`) if not followed by P in `P1'`. It will not cleave after W followed by M in `P1'`. It will not cleave after M followed by Y in `P1'`. It will not cleave after H followed by D/M/W in `P1'`.
 
 **RPG definition:**
 
@@ -345,7 +349,7 @@ https://web.expasy.org/peptide_cutter/peptidecutter_enzymes.html#Chym
 Clostripain
 ...........
 
-Clostripain (Clostridiopeptidase B) preferentially cleaves after R.
+Clostripain (Clostridiopeptidase B) preferentially cleaves after R (`P1`).
 
 **RPG definition:**
 
@@ -363,7 +367,7 @@ https://web.expasy.org/peptide_cutter/peptidecutter_enzymes.html#Clost
 CNBr
 ....
 
-CNBr preferentially cleaves after M.
+CNBr preferentially cleaves after M (`P1`).
 
 **RPG definition:**
 
@@ -381,7 +385,7 @@ https://web.expasy.org/peptide_cutter/peptidecutter_enzymes.html#CNBr
 Enterokinase
 ............
 
-Enterokinase preferentially cleaves after K preceded by D/E in `P2`, `P3`, `P4` and `P5`.
+Enterokinase preferentially cleaves after K (`P1`) preceded by D/E in `P2`, `P3`, `P4` and `P5`.
 
 **RPG definition:**
 
@@ -399,7 +403,7 @@ https://web.expasy.org/peptide_cutter/peptidecutter_enzymes.html#Enter
 Factor Xa
 .........
 
-Factor Xa preferentially cleaves after R preceded by G in `P2`, D/E in `P3` and A/F/I/L/V/W/G/T in `P4`.
+Factor Xa preferentially cleaves after R (`P1`) preceded by G in `P2`, D/E in `P3` and A/F/I/L/V/W/G/T in `P4`.
 
 **RPG definition:**
 
@@ -417,7 +421,7 @@ https://web.expasy.org/peptide_cutter/peptidecutter_enzymes.html#Xa
 Glu-C
 .....
 
-Glu-C Sequencing Grade preferentially cleaves after D or E.
+Glu-C Sequencing Grade preferentially cleaves after D or E (`P1`).
 
 **RPG definition:**
 
@@ -435,7 +439,7 @@ https://france.promega.com/resources/pubhub/using-endoproteinases-asp-n-and-glu-
 Lys-C
 .....
 
-LysC Lysyl endopeptidase (Achromobacter proteinase I) preferentially cleaves after K.
+LysC Lysyl endopeptidase (Achromobacter proteinase I) preferentially cleaves after K (`P1`).
 
 **RPG definition:**
 
@@ -452,7 +456,7 @@ More informations: https://web.expasy.org/peptide_cutter/peptidecutter_enzymes.h
 Lys-N
 .....
 
-LysN Peptidyl-Lys metalloendopeptidase preferentially cleaves before K.
+LysN Peptidyl-Lys metalloendopeptidase preferentially cleaves before K (`P1'`).
 
 **RPG definition:**
 
@@ -469,7 +473,7 @@ More informations: https://web.expasy.org/peptide_cutter/peptidecutter_enzymes.h
 NTCB
 ....
 
-NTCB +Ni (2-nitro-5-thiocyanobenzoic acid) preferentially cleaves before C.
+NTCB +Ni (2-nitro-5-thiocyanobenzoic acid) preferentially cleaves before C (`P1'`).
 
 **RPG definition:**
 
@@ -486,7 +490,7 @@ More informations: https://web.expasy.org/peptide_cutter/peptidecutter_enzymes.h
 Pepsin pH 1.3
 .............
 
-This pepsin preferentially cleaves around F or L. It will not cleave before F or L followed by P. It will not cleave before F or L preceded by R in `P2` or P in `P3` or H/K/R in `P4`. It will not cleave after F or L followed by P in `P2'`. It will not cleave after F or L preceded by P in `P2` or H/K/R in `P3`.
+This pepsin preferentially cleaves around F or L (`P1` or `P1'`). It will not cleave before F or L in `P1'` followed by P in `P2'`. It will not cleave before F or L in `P1'` preceded by R in `P1` or P in `P2` or H/K/R in `P3`. It will not cleave after F or L in `P1` followed by P in `P2'`. It will not cleave after F or L in `P1` preceded by P in `P2` or H/K/R in `P3`.
 
 **RPG definition:**
 
@@ -513,7 +517,7 @@ More informations: https://web.expasy.org/peptide_cutter/peptidecutter_enzymes.h
 Pepsin pH >=2
 .............
 
-This pepsin preferentially cleaves around F, L, W or Y. It will not cleave before F, L, W or Y followed by P. It will not cleave before F, L, W or Y preceded by R in `P2` or P in `P3` or H/K/R in `P4`. It will not cleave after F, L, W or Y followed by P in `P2'`. It will not cleave after F, L, W or Y preceded by P in `P2` or H/K/R in `P3`.
+This pepsin preferentially cleaves around F, L, W or Y (`P1` or `P1'`). It will not cleave before F, L, W or Y in `P1'` followed by P in `P2'`. It will not cleave before F, L, W or Y in `P1'` preceded by R in `P1` or P in `P2` or H/K/R in `P3`. It will not cleave after F, L, W or Y IN `P1` followed by P in `P2'`. It will not cleave after F, L, W or Y in `P1` preceded by P in `P2` or H/K/R in `P3`.
 
 **RPG definition:**
 
@@ -540,7 +544,7 @@ More informations: https://web.expasy.org/peptide_cutter/peptidecutter_enzymes.h
 Thrombin (PeptideCutter)
 ........................
 
-This thrombin preferentially cleaves after R. Optimum cleavage is when R is preceded and followed by G. Cleavage also occurs when R is preceded by P in `P2` and A/F/I/L/V/W/G/T in `P3` and `P4`. It will not cleave after R followed by D/E in `P1'` or `P2'`.
+This thrombin preferentially cleaves after R (`P1`). Optimum cleavage is when R is preceded and followed by G (`P2` and `P1'`). Cleavage also occurs when R is preceded by P in `P2` and A/F/I/L/V/W/G/T in `P3` and `P4`. It will not cleave after R followed by D/E in `P1'` or `P2'`.
 
 It not strictly coherent with the definition as differences exist in PeptideCutter between definition, summary and behavior of this enzyme.
 
@@ -567,9 +571,9 @@ More informations: https://web.expasy.org/peptide_cutter/peptidecutter_enzymes.h
 Thrombin Sequencing Grade
 .........................
 
-This thrombin preferentially cleaves after R preceded by P in `P2`, V in `P3` and L in `P4` and followed by G in `P1'` and S `P2'`.
+This thrombin preferentially cleaves after R (`P1`) preceded by P in `P2`, V in `P3` and L in `P4` and followed by G in `P1'` and S `P2'`.
 
-This thrombin is defined in several kit (see links)
+This thrombin is defined in several kit (see below).
 
 **RPG definition:**
 
@@ -590,9 +594,7 @@ More informations: see thrombin cleavage kit of
 Trypsin
 .......
 
-Trypsin preferentially cleaves after K or R. It will not cleave after K followed by P in `P1'` except if W in `P2`. It will not cleave after R followed by P in `P1'` except if M in `P2`. It will not cleave CKD, DKD, CKH, CKY, CRK, RRH nor RRR
-
-This thrombin is defined in several kit (see links)
+Trypsin preferentially cleaves after K or R (`P1`). It will not cleave after K followed by P in `P1'` except if W in `P2`. It will not cleave after R followed by P in `P1'` except if M in `P2`. It will not cleave CKD, DKD, CKH, CKY, CRK, RRH nor RRR.
 
 **RPG definition:**