A trypsin and chymotrypsin inhibitor from groundnuts (Arachis hypogaea)

Purification, characterization and immunolocalization of a novel protease inhibitor from hemolymph of tasar silkworm, Antheraea mylitta

A novel serine protease inhibitor (AmPI) was purified from larval hemolymph of tasar silkworm, Antheraea mylitta by two-step process of trypsin-affinity and gel-filtration (FPLC) chromatography. AmPI was active against larval midgut and commercial bovine trypsin and chymotrypsin. The extent of purification was determined by SDS and Native PAGE. The protease inhibitor had an apparent molecular weight of approximately 14.5 kDa as determined by SDS-PAGE. Its activity was stable over a pH range of 4.5-9 and temperatures range of 4-65 degrees C. Molecular weight as determined by MALDITOF-MS was between 13241.63 and 13261.66 Da. MS profile of AmPI also suggests two isoforms of AmPI because of glycosylation by heptose (C(7)H(14)O(7)). This confirmed the result of Native PAGE showing two bands. N-terminal amino acid sequence of this protein did not show similarity to any known protease inhibitor. To study the functional implications of AmPI in insect, it was localized in insect body tissue of different larval instars by immunogold labeling technique using GAR-gold conjugate as secondary antibody. The pattern of localization suggests constitutive nature of AmPI, which may have role in insect's defense mechanism.

Nutritional improvement of legume proteins through disulfide interchange

Treatment of raw soy flour with L-cysteine or N-acetyl-L-cysteine results in the introduction of new half-cystine residues into sulfur-poor legume proteins, with a corresponding improvement in nutritional quality as measured by the protein efficiency ratio (PER) in rats. The proteins are modified through formation of mixed disulfide bonds among added sulfhydryl compounds, proteolytic enzyme inhibitors, and structural legume proteins. This modification leads to loss of inhibitory activity and increased protein digestibility and nutritive value. Sodium sulfite is more effective than cysteine in facilitating inactivation of trypsin inhibitors in soy flour. The synergistic effect of sodium sulfite and heat may be due to ability to induce rearrangement of protein disulfide bonds to produce new structural entities without altering the amino acid composition and to the fact that the new structures lose their ability to complex with trypsin or chymotrypsin. The same treatment inactivated hemagglutinins (lectins) in lima bean flour. These considerations suggest a key role for sulfur amino acids in the nutritional quality and safety of legumes.

Plant inhibitors of proteolytic enzymes

The presence of inhibitors of proteinases was stated in many species of plants. There are macropeptides of the molecular weight ranging from 3700 to 8000, often bound to carbohydrates. Potential sources of inhibitors of proteinases are legumes, cereals, potatoes and also some fruits. They are characterized by different activity. "Single-headed" inhibitors inhibit one type of proteolytic enzyme, when "double-headed" inhibitors, possessing two independent active sites, can inhibit several types of proteolytic enzymes at the same time. They also differ in the resistance to temperature and change of pH. The role and importance of inhibitors of proteinases is not exactly explained. They are used in the pharmaceutical, baking and beer-industry as well as in the therapy of numerous diseases.

Inhibitors of acrosomal proteinase as antifertility agents. A problem of acrosomal membrane permeability

In vitro studies were performed to investigate the accessibility of acrosin to various proteinase inhibitors inside the intact acrosome of testicular, ejaculated, and uterine human spermatozoa. As test system the gelatin plate assay was used. For this assay it was shown formerly that a correlation exists between the size of the digested lysis areas (halo formation) and acrosin activity estimated with synthetic substrates. In addition, saturation of the gelatin substrate membranes with acrosin inhibitors including highly specific ones before application of spermatozoa completely prevented halo formation indicating that the gelatinolytic activity of human spermatozoa is caused exclusively by acrosin. When human spermatozoa were incubated with various acrosin inhibitors (concentration: 1 mmol/l) prior to application to the gelatin membrane, reduction of halo formation could not be observed, however. This result indicates that most of the tested acrosin inhibitors (9 naturally occurring protein inhibitors, 2 microbial peptide inhibitors, 19 synthetic inhibitors) were unable to penetrate the acrosomal membranes of testicular, ejaculated, and uterine human spermatozoa. Only 2 inhibitors caused moderate up to complete inhibition of the gelatinolytic activity of the spermatozoa if applied in concentrations between 1 and 10 mmol/l: the proteinase inhibitor aprotinin and the synthetic inhibitor NPGB (4-nitrophenyl 4-guanidinobenzoate). Obviously, human acrosomal membranes seem to be especially impenetrable to proteins, polypeptides, and synthetic agents. Those acrosin inhibitors penetrating the human sperm head membranes are either too toxic or the local concentration necessary for effective acrosin inhibition in vivo cannot be achieved within the male or female genital tract secretions. Therefore, acrosin inhibitors cannot be used for human contraception at present. Thus it is mandatory to continue the search for suitable acrosin inhibitors with low toxicity easily penetrating into the intact sperm acrosome.

Purification, some properties and the complete primary structures of two protease inhibitors (DE-3 and DE-4) from Macrotyloma axillare seed

The Macrotyloma axillare plant, belonging to the Leguminosae family, is a perennial climbing or trailing herb 0.2--3.5 m long. The plant is indigenous to South Africa and it occurs in the warm dry northern parts of the Transvaal. It has been introduced into Australia, where the seed are used as animal food. Two protease inhibitors, DE-3 and DE-4, were purified from Macrotyloma axillare seed by gel filtration on Sephadex G-50 followed by ion-exchange chromatography on DEAE-cellulose. They each comprise 76 amino acid residues including 14 half-cystine residues. The complete primary structures of the two protease innibitors have been elucidated and their sequences are 67% identical. The inhibitor specificities, the sequences, the invariant amino acid residues and the reactive inhibitor sites of protease inhibitors DE-3 and DE-4 resemble the corresponding properties of the Bowman-Birk double-headed protease inhibitor group. The cysteine residues are in similar locations to those in protease inhibitors of known structure so they are presumed to link similarly.