Reflux Revisited: Advancing the Role of Pepsin

Table 1

The active pepsin isoenzymes in man.

Pepsin isoenzyme	Proportion of total pepsin	Substrate: pH optimum range	Molecular; weight (Da)	Comments
1	<5%	Haemoglobin: 1.9; Collagen: 3.0; Mucin: 2.0	43810	The proportion of pepsin 1 rises to 23% in DU; Mucolytic pepsin; Complexed with carbohydrate
2	<1%	Haemoglobin: 2.1	39950
3	80%	Haemoglobin: 2.4–3.1	37150	Pepsin 3 is a complex of isoenzymes. The assay measures their combined effects.
3A; 3B; 3C	6%; 70%; 4-5%	Haemoglobin: 3.2		3A is structurally similar to 3B but is phosphorylated
5 (Gastricsin)	6-7%	Haemoglobin: 2.0–3.6 (maximum at 3.2) Mucin: 3.5–5	31620	Stable up to pH 7.3

“Pepsin 4” is a complex of pepsin and an inhibiting peptide, hence, it does not appear in the list of active pepsin isoenzymes.
“Pepsin 6” is the remnant of a zymogen, in all probability pepsinogen, hence it too does not feature in the isoenzyme list.
“Zone 7” was found to be a cathepsin.
References [21–25].