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Isracidin [id=CAA0001]

Synonym: Alphas1-casein (16-38)

Producer Organism : Native Protein : Production Method :
Cow αs1-casein Enzymatic hydrolysis and TCA treatment
Activity : Antibacterial
Target Organisms :

Gram-positive: Lactobacillus sp. (no MIC).

NOTE: No activity against Pseudomonas aeruginosa, Candida albicans (>1 mg/ml) .

Description :
Production method: Chymosin hydrolysis then TCA treatment.

Isracidin was found to inhibit the in vitro growth of lactobacilli, which led to study of its broader antibacterial action. In vitro bactericidal effects were found against a variety of Gram-positive bacteria, but only at the high concentrations of 0.1-1 mg/ml (Citation: 2).
Length : 23 Mass (Da): 2 764.95 Common Amino Acids : L
Isolectric Point : 10.77 Net Charge : 4 Absent Amino Acids : ACDMSTWY
Basic Residues : 6 Acidic Residues : 2 Hydrophobic Residues : 7
Polar Residues : 3 Boman Index : -55.68 Hydropathy Index : -0.987
Aliphatic Index : 97.39 Instability Index : 0 Extinction Coefficient :
Absorbance 280nm : 0

Wheel representation

Hydrophobicity plot

Red solid plot : values according to the hydrophobicity scale of Kyte and Doolittle (reference paper).
Yellow dashed plot : Experimentally determined hydrophobicity scale for proteins at membrane interfaces(reference paper).
Green dotted-dashed plot : prediction of transmembrane helices (reference paper). In this scale (unlike the others), more negative values reflect greater hydrophobicity.

Multiple Sequence Alignment (MSA)


1 CAA0001 100.0%  RPKHPIKHQGLPQEVLNENLLRF 

2 CAA0003 100.0%  -----IKHQGLPQE--------- 
3 CAA0004 100.0%  --------------VLNENLLR- 

Citation: 1

Antibacterial and immunostimulating casein-derived substances from milk: casecidin, isracidin peptides

Cited Entries: CAA0001

Authors:Lahov, E., Regelson, W.
Journal: Food and Chemical Toxicology 1996, 34(1).
CrossRef External Link
Abstract: Apart from immunoglobulin A and G antibodies and plasma cells, milk also contains antibiotic/host protective peptides that are of value not only for maintenance of its nutritional integrity but also for protection of the newborn and, possibly, protection of the lactating mother. Among the first such peptides identified with casecidin; following chymosin digestion of casein at pH 6 or 7, casecidin inhibited in vitro staphylococci, sarcina, Bacillus subtilis, Diplococcus pneumoniae and Streptococcus pyogenes. Inhibition occurred at high concentrations, in vitro, compared with commercial antibiotics, and thus interest in casecidin languished. Work with casecidin was followed by investigation of a related refined non-immunogenic product of chymosin digestion of alpha s1-casein. This product consisted of the N -terminal segment (1-23) of alpha s1-casein B, named "isracidin", and was significantly effective in vivo at concentrations that were competitive with known antibiotics, as seen in the protection of mice against lethal infection by Staphylococcus aureus strain Smith. Field trials showed that injection of isracidin into the udder gave protection against mastitis in sheep and cows. Isracidin was both therapeutic and prophylactic and responses to its therapeutic effect produced long-term immune resistance. Isracidin protected mice against Candida albicans, by stimulation of both phagocytosis and immune responses. However, like other recently described milk-derived peptides, despite its clinical value, isracidin was overlooked because of the lack of commercial interest in the 1970s and early 1980s, in host-mediated non-specific resistance as a therapeutic approach to infection. Another problem that impeded commercial interest was the isomeric variation in isracidin peptides seen on a large-scale batch production for commercial use. It is hoped that this review of previous studies of the activity of isracidin action will revive interest in milk as an antibiotic source.
Citation: 2

A rennin-sensitive bond in alphas1 B-casein

Cited Entries: CAA0001

Authors:Hill, R.D., Lahav, E., Givol, D.
Journal: Journal of Dairy Research 1974, 41(01).
Abstract: Rennin acts on a specially sensitive bond in αs1 B-casein to produce a basic peptide containing residues 123 of the original protein. At pH 64 and 30C, the action is specific and rapid, the kinetic constants being Km 4510−4M, Kcat 38 s−1, and kcat/Km 085104 s−1 M−1. Pepsin, and a protease impurity in the acid phosphatase from wheat germ, have a similar action.

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