The venom of the black mamba contains a

The screening of a bovine submaxillary gland cDNA library yielded 25 clones coding for bovine lactotransferrin. The nucleotide sequence of the longest insert contained a protein-coding region of 21 15 nucleotides and a 3' non-coding region of 194 nucleotides followed by a poly(A) tract of about 55 nucleotides. The predicted peptide sequence included a 16-amino-acid signal sequence upstream of the first amino acid of the native protein.The identity of the clone was confirmed by matching the amino acid sequence predicted from the cDNA with the N-terminal and tryptic peptide sequences derived from purified bovine milk lactotransferrin, and also by similarity with human and murine lactotransferrins. The cDNA described corresponds to a 705-amino-acid-long preprotein that lacks the start methionine. The sequence of the secreted protein is 689 amino acids long and contains five potential glycosylation sites. Bovine lactotransferrin is 69% and 64% identical to human and murine lactotransferrins, respectively.The transferrins are a family of non-haem, iron-binding proteins which includes serum transferrin, lactotransferrin and melanotransferrin. They are monomeric glycoproteins with a molecular mass of about 80 kDa constituted by two lobes, each possessing one iron-binding site with the capacity to bind reversibly one ferric ion (Fe3+) (reviewed in [l, 21). Lactotransferrins (also called lactoferrins) are present in various biological fluids such as human milk [3 -51, bovine milk [6], saliva [7, 81 and mucous secretions [8, 91. They are also present in leucocytes [S, 10, 111. Although lactotransferrins were first isolated in 1960 from both human and bovine milk, most of the studies concerning their structure and biological roles (reviewed in [l, 21 and [12 -141) were performed on the human protein. The sequence of human lactotransferrin was resolved using chemical methods [15] and cDNA analysis [16] (and cited by Anderson et al. in [17]). It consists of a 691-amino-acid polypeptide chain to which two biantennary glycans of the N-acetyllactosaminic type are linked [18]. This sequence is 70% identical to the sequence of murine lactotransferrin recently determined by cDNA sequencing [19] and resolved as a 688-amino-acid polypeptide chain to which a single glycan of the N-acetyllactosaminic type is conjugated 1201.The only information known about the primary structure of bovine lactotransferrin concerned its N-terminal amino acid sequence APRKNVRWXTISQPE [21] and its carboCorrespondence to A.