The amino acid sequence of a recently isolated camel milk protein rich in half-cystine has been determined by peptide analyses. The 11 7-residue protein has 16 half-cystine residues, concluded to correspond to disulfide bridges and suggesting a tight conformation of the molecule.Comparisons of the structure with those of other proteins reveal several interesting relationships. The camel protein is clearly homologous with a previously reported rat whey phosphoprotein of possible importance for mammary gland growth regulation, and with a mouse protein of probable relationship to neurophysins. The camel, rat and mouse proteins may represent species variants from a rapidly evolving gene. Residue identities in pairwise comparisons are 40% for the camel/rat proteins and 33% for the camel/mouse proteins, with 38 positions conserved in all three forms. The camel protein also reveals an internal repeat pattern similar to that for the other two proteins.The homology between the three milk whey proteins has wide implications for further relationships. Thus, previously noticed similarities, involving either of the milk proteins, include limited similarities to casein phosphorylation sites for the camel protein, to neurophysins in repeat and half-cystine patterns for the mouse and rat proteins, and to an antiprotease for the rat protein. These similarities are reinforced by the camel protein structure and the recognition of the three whey proteins as related. Finally a few superficial similarities with the insulin family of peptides and with some other peptides of biological importance are noticed. Combined, the results relate the camel protein in a family of whey proteins, and extend suggestions of relationships with some binding proteins.

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A milk protein, occurring in the whey fraction, has been characterized from camel milk. Determination of the primary structure reveals the existence of two related types of chain with residue differences in at least the N-terminal region. A fragment representing an N-terminal part of the protein was also recovered (heterogeneous at the same positions). The absence of cysteine residues in the protein shows that no disulphide bridges are present. The pattern of fragments and a parent protein resembles that for casein and its fragments, showing that fragments and a multiplicity of forms may be typical for different milk proteins.

A small protein (Mr about 14 000) rich in cysteine/half-cystine has been isolated from camel milk by exclusion chromatography and reverse-phase high-performance liquid chromatography. The N-terminal amino acid sequence shows a region with several positional identities with alpha and beta-caseins, which however lack cysteine residues; positions 16-20 are identical and involve the serine residues that have been found to be phosphorylated in beta-caseins.

A trypsin inhibitor from the venom of the cobra Nuja nuju nuja has been isolated by a single step of reversephase high-performance liquid chromatography. The protein strongly inhibits trypsin (Ki = 3.5 pM). The primary structure was determined by peptide analysis of the [ ''C]carboxymethylated inhibitor. The 57-residue polypeptide chain belongs to the family of Kunitz-type inhibitors, and exhibits 42% residue identity with bovine pancreatic trypsin inhibitor. The structure shows only 70% identity with the corresponding peptide from the Capa cobra (Naju neviu), establishing that the inhibitor molecule exhibits extensive variations. Functionally, a basic residue at position P3' correlates with strong inhibition.Basic protease inhibitors of the serine proteases are abundant in nature and appear to be present in all forms of life [l]. Different types have been isolated and extensively studied. Based on different properties, they have been classified into at least seven families [2].Studies of snake venoms reveal the presence of several protease inhibitors, particularly from Elapidae and Viperidae snakes. These inhibitors belong to the protein family of pancreatic trypsin inhibitors of the Kunitz type [3]. The amino acid sequences of the venom inhibitors from Viperu russelli (Russell's viper) [4], Nuju neviu (Cape cobra) [5], Dendroaspis polylepis (black mamba) [6], Vipera ummodytes (long-nosed viper) [7] and Hemachatus haemuchutus (Ringhalls cobra) [5] have been characterized. These analyses, correlated with the known tertiary structure of the pancreatic inhibitor [S], have facilitated understanding of the structure/function relationships for the inhibitors. Comparisons show conservation of residues at both the site of the main contacts with serine proteases [9] and the region of weak contacts [S]. The snake venom inhibitors can inhibit the activities of serine proteases, including bovine trypsin, kallikrein and plasmin [7].During investigation of the venom of the nominate race of cobra, Naja naja naja (from Pakistan), we have isolated a highly potent trypsin inhibitor of this venom. In this work, we report a single-step purification of the inhibitor on reversephase HPLC, enzymatic parameters for the protease inhibition, and the primary structure of the inhibitor, explaining its potency and antitrypsin activity.

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Two disulfide-rich, low-molecular mass peptides (-3 kDa and -4 kDa) have been isolated from Buthus sindicus venom using ion-exchange and reverse-phase HPLC. Peptide I has 35 residues with 8 half-cystine residues and is clearly related to four-disulfide core proteins of the neurophysin type and to toxins of other scorpion species (5563% residue identity). Peptide II, present in low yield, has 28 residues with 6 half-cystine residues and a structure Iargely dissimilar from that of peptide I and other characterized toxins, although probably still a member of the disulfide core peptide type. Consequently, scorpion venom contains, in addition to toxins characterized before, toxin-like compounds with distant relationships.