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Chitin is a major component of the cuticle of arthropods. However, the synthesis of chitin is poorly understood. Feeding larvae of the insect Lucilia cuprina on the fungal chitin synthase competitive inhibitor, nikkomycin Z resulted in strong concentration-dependent mortality of the larvae (LD50 = 280 nM). This result demonstrates that chitin is an essential component of this insect. The complete cDNA and deduced amino-acid sequences of the first arthropod chitin synthase-like protein, LcCS-1, from the larvae of the insect L. cuprina have been determined. The cDNA sequence is 5757 bp in length and codes for a large complex protein containing 1592 amino acids (Mr = 180 717). Analysis of the whole protein sequence reveals low, but significant, similarity to yeast chitin synthases with stronger areas of conservation centred on local regions implicated in the active sites of the yeast enzymes. Strikingly, LcCS-1 contains 15-18 potential transmembrane segments, indicating that the protein is an integral membrane protein. Two alternative topographical models of LcCS-1 are described, which involve its association with either the plasma membrane or the membrane of intracellular vesicles. LcCS-1 mRNA is produced in all life stages of the insect with expression in the larval stage limited to the integument and trachea. In a third instar larva the mRNA was localized to a single layer of epidermal cells immediately underlying the procuticle region of the integument. cDNA or genomic sequences that are highly related to fragments of LcCS-1 were demonstrated in three insect orders, one arachnid and Caenorhabditis elegans, thereby attesting to the importance of this enzyme in these chitin-producing organisms. Bioinformatics has been used to deduce the gene sequence and organization of the highly homologous Drosophila melanogaster orthologue of LcCS-1, DmCS-1.

An antigen, BMA7, which induced partial immunity against tick infestation has been isolated from Boophilus microplus using two different protein fractionation protocols, accompanied by vaccination and parasite challenge trails. The antigen is a 63 kDa glycoprotein isolated from semi-engorged adult female ticks. Though significant, the induced immunity is less striking than that previously reported for antigen Bm86 from the same parasite. However, co-vaccination with Bm86 and BMA7 can enhance immunity over that seen with a commercial vaccine based on Bm86 alone. Limited peptide sequence information shows significant variation in the BMA7 protein occurs. The antigen has approximately 36 kDa of glycosylation, in both N-linked and O-linked oligosaccharides. There is evidence that both polypeptide and oligosaccharide are antigenic, but the chemical nature of the protective antigenic sites is not clear. There is little or no immunological response to the antigen during natural infestation with parasites, suggesting the antigen is 'concealed' and protective immunity dependent on artificial vaccination. The antigen has some similarities with the vertebrate mucins. It is widely distributed in tick tissues and membrane bound but its function is currently unknown.

A protein, Bm91, which was first identified as a protective vaccine antigen from the tick Boophilus microplus, has regions of very strong amino acid sequence similarity to mammalian carboxydipeptidases or angiotensin converting enzymes (ACE; E.C. 3.4.15.1). This protein is now shown to share many biochemical and enzymatic properties with mammalian carboxydipeptidases. It is enzymatically active in a conventional assay for ACE using hippuryl-Gly-Gly as substrate. The hydrolysis of the C-terminal nonapeptide of the insulin B chain proceeds by sequential removal of carboxy-terminal dipeptides. The similarities extend to the dependence of activity on pH and added salt. Bm91 is inhibited by two well-characterized inhibitors of the mammalian enzymes, the drug Captopril and a nonapeptide, and the inhibition occurs in similar concentration ranges to those effective with the mammalian enzymes. However, the natural substrates of the tick enzyme are unknown. Angiotensin I itself is a poor substrate and the enzyme's natural substrates are likely to be one or more of the pharmacologically active peptides occurring in insects and arthropods.

Boophilus microplus contains a nucleotidase-like enzyme which is able to hydrolyze a range of nucleoside 5'-mono-, di- and triphosphates to the nucleoside. Its relationship to several other nucleotide hydrolyzing enzymes has been explored. Limited peptide sequencing shows similarities to both mammalian nucleotidases and the Escherichia coli uridine diphosphate sugar hydrolase. The tick enzyme also hydrolyzes UDP-glucose, though by a mechanism different to that of the bacterial enzyme. On the other hand, it resembles the mammalian nucleotidases in that there is evidence that it is attached to the cell membrane by a glycosyl-phosphatidylinositol (GPI) anchor.