Amino acid and protein metabolism

Selective cleavage of pepsin by molybdenum metallopeptidase

In this study, the cleavage of protein by molybdenum cluster is reported for the first time. The protein target used is porcine pepsin.

The data presented in this study show that pepsin is cleaved to at least three fragments with molecular weights of ca 23, ca 19 and ca 16 kDa when the mixture of the protein and ammonium heptamolybdate tetrahydrate ((NH4)6Mo7O24.4H2O) was incubated at 37 degrees C for 24 h. No self cleavage of pepsin occurs at 37 degrees C, 24 h indicating that the reaction is mediated by the metal ions.

N-terminal sequencing of the peptide fragments indicated three cleavage sites of pepsin between Leu 112-Tyr 113, Leu 166-Leu 167 and Leu 178-Asn 179.

The cleavage reaction occurs after incubation of the mixture of pepsin and (NH4)6Mo7O24.4H2O for only 2 h. However, the specificity of the cleavage decreases when incubation time is longer than 48 h.

The mechanism for cleavage of pepsin is expected to be hydrolytic chemistry of the amide bonds in the protein backbone. (C) 2012 Elsevier Inc. All rights reserved

Yenjai, S., Malaikaew, P., Liwporncharoenvong, T., and Buranaprapuk, A., Selective cleavage of pepsin by molybdenum metallopeptidase, Biochemical and Biophysical Research Communications, 2012, 419, 126-129.

At low concentrations molybdenum has a beneficial effect on animal growth and protein synthesis in some species. Chicks grew more rapidly and had a higher haemoglobin count when 1-5 ppm Mo was added to the diet [Humphries, 1970; Norris, 1969; Probst, 1971]. The improvement in growth did not occur with diets containing 100 ppm Mo indicating some toxicity at this higher level. Molybdenum promotes protein synthesis in the red trout [Jurca and Matei, 1967]. Trout raised on a diet which included 0.126 g ammonium molybdate/100 kg forage were larger and better developed than those raised on fresh food and the protein content of the blood serum was increased. However, according to other work molybdenum may have an inhibitory effect on protein synthesis. Molybdenum (400 ppm) added to the diet of experimental rats did not affect digestion and absorption of nitrogen compounds but caused an increase in urinary excretion first as urea and ammonia and then as alpha-amino nitrogen [Johnson and Miller, 1963; Val chuk and Kovalskaya, 1970]. Urinary levels of alpha-amino nitrogen increased with increased dietary molybdenum and with increased time of feeding, and urea and ammonia decreased. Molybdenum inhibited incorporation of leucine into protein in a homogenised rat liver preparation (16% inhibition at 10-4 M Mo and 80% inhibition at 10-3 M) [Peive, 1968].

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