Inhibition of porcine elastase II by chicken ovoinhibitor

The chicken pituitary expresses an ovoinhibitor-like protein in subpopulations of some, but not all, hormone-producing cell types

Ovoinhibitor is a serine protease-inhibiting protein that was originally purified from egg whites. It is secreted by the oviduct under the control of estrogen and progesterone and it specifically inhibits serine proteinases such as trypsin and chymotrypsin. During recent attempts to raise monoclonal antibodies (Mabs) against chicken bursa of Fabricius proteins, one Mab was produced that specifically recognized chicken ovoinhibitor. This was the first demonstration of ovoinhibitor in an avian immune organ. We presently report on the expression of an ovoinhibitor-like molecule by the pituitary of the chicken as revealed by immunocytochemistry and RT-PCR. Immunofluorescent dual staining experiments using the mouse anti-ovoinhibitor Mab in conjunction with polyclonal antibodies against various hypophysial hormones revealed partial co-localization of an ovoinhibitor-like molecule with growth hormone (GH), luteinizing hormone (LH), and pro-opiomelanocortin (POMC), in a subset of the respective hormone producing cells. By contrast, no co-localization with prolactin (PRL) could be reliably demonstrated. RT-PCR of hypophysial mRNA using ovoinhibitor gene-specific primers yielded an amplicon that was 20% shorter than predicted on the basis of the published ovoinhibitor sequence. Sequencing revealed that of the represented exons only the central portion was expressed in the pituitary and that both 5' and 3' ends of each exon had been truncated. While expression of ovalbumin-like serine protease inhibitors (serpins) has been previously reported in the rat pituitary, to our knowledge, this is the first report of a Kazal-type serine protease inhibitor in the vertebrate neuroendocrine system.

Partial amino acid sequence of porcine elastase II. Active site and the activation peptide regions

The partial amino acid sequence of porcine elastase II, isolated from crude trypsin Type II, was determined. The enzyme consists of two polypeptide chains, a light chain composed of 11 residues, and a heavy chain (Mr = 23 500) with four intrachain disulfide bridges; the two chains are held together by one interchain disulfide bond. Elastase II was fragmented into several peptides by chemical cleavages with CNBr at the two methionine residues, 99 and 180 (chymotrypsinogen numbering), and with hydroxylamine at the peptide bond following DIP-Ser195. About 50% of the sequence was determined and the positions of 120 amino acids were located, including the light chain residues and most of the active site residues. The partial sequence shows 64% difference between porcine elastase II and elastase I and only 26% difference between porcine elastase II and bovine chymotrypsin B.

Digestion of elastin by porcine pancreatic elastase I and elastase II

Elastin was fully solubilized by digestion with elastase I or elastase II. Each digest was separated into high-molecular weight and low-molecular weight fractions that were characterized by the correspondence to their amino acid content, N-terminal sequence and C-terminal amino acids. It was found that although the relative amount of amino acids in the low-molecular weight fraction obtained by digestion with elastase I was lower than in digestion with elastase II, no major difference in the type of bonds cleaved in the low- or high-molecular weight fractions of each digest could be seen. There is, however, a remarkable difference in the type of bond cleaved by the two enzymes. While elastase I cleaves mostly Ala-Ala and also Ala-Gly bonds, elastase II hydrolyzes Leu-Ala, Leu-Gly, Phe-Ala, Phe-Gly and Tyr-Ala, Tyr-Gly bonds. Theoretical calculations led us to suggest both digests are composed of cross-linked peptides that vary not only in the molecular size but also in the number of cross-links found in peptides of the same size.

Purification and properties of protease F, a bacterial enzyme with chymotrypsin and elastase specificities

It has been previously demonstrated that commercial bacterial fibrinolysin (EC 3.4.21.7) selectively cleaves the bond between Met-53 and Ala-54 in ovine prolactin (199 amino acids). A one-step purification procedure on DEAE-cellulose for Protease F, which is the active component of bacterial fibrinolysin, and properties of the purified enzyme are reported. The enzyme is homogeneous as judged by acrylamide gel electrophoresis. Its molecular weight, calculated from gel filtration experiments on Sephadex G-100, is around 13,800. Amino acid analyses do not reveal the presence of any half-cystines. The presence of one tryptophan residue per enzyme molecule was resolved from the fluorescence spectrum. Amino terminal analysis showed that leucine was at the amino terminal position. Protease F hydrolyzes casein and synthetic specific substrates for chymotrypsin and elastase esterases but not for trypsin esterases. It is fully inhibited by phenylmethylsulfonyl fluoride, by chicken ovoinhibitor, and by Chymotrypsin Inhibitor I from potatoes but not by the trypsin-chymotrypsin inhibitors from soybeans and chick peas or by tosyl-L-phenylalanine chloromethyl ketone. The enzyme is stable at room temperature and in the cold, it is not affected by dialysis or by freezing and thawing, but it is inactivated during freeze-drying. The circular dichroism spectra of Protease F indicate an approximate 20% alpha-helix content of the enzyme with a considerable similarity to those of subtilisin, elastase, and beta-trypsin. The relatively low molecular weight of Protease F, the absence of intrachain disulfide bridges, and the fact that it is inhibited by several, but not all, chymotrypsin inhibitors suggest that it may differ phylogenetically from the known serine proteases.