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Crotoxin and homologous crotalid presynaptic neurotoxins consist of a toxic, basic subunit and a slightly smaller, nontoxic, acidic subunit. The latter, in turn, consists of three chains, interconnected by disulfide bonds. The complete sequences of two of the three acidic subunit chains of crotoxin, from the venom of the South American rattlesnake Crotalus durissus terrificus, have been determined. In addition, all but the ten amino-terminal residues of the third chain have been sequenced. Sequence comparison data suggest that the acidic subunit has been derived from a nontoxic, homodimeric, crotalid phospholipase A2. When compared with sequences of phospholipases A2, the acidic subunit lacks a 22-residue amino-terminal segment and two additional segments that are implicated in phospholipid substrate binding. However, it apparently retains an intact active site, the calcium binding loop, and segments involved in subunit binding in homodimeric phospholipases A2. The C chain of the acidic subunit shows strong homology with mammalian neurophysins, lending possible support to the hypothesis that the acidic subunit functions as a chaperone to prevent nonspecific binding of the toxic basic subunit. Crystals suitable for X-ray diffraction studies have recently been produced [Achari, A., Radvanyi, F. R., Scott, D., Bon, C., & Sigler, P. B. (1985) J. Biol. Chem. 260, 9385-9387]; thus with these data it should now be possible to determine the three-dimensional structure of the intact neurotoxin and dissociated subunits.

Near-infrared spectral absorption properties were determined for emulsified and ground meat samples. Six corrected log numbers associated with the optical responses of 6 filters in the InfraAlyzer were used as multiple independent variables in regression equations. Dependent variables for the equations were moisture, determined by oven-drying; fat, determined by Goldfisch extraction; and protein, determined by the Kjeldahl method. InfraAlyzer log values, replicated 4 times on each emulsified beef sample and 3 times on each ground lamb sample, increased as the samples were warmed from the heat generated in the sample drawer. Variation in temperature of the meat samples was partially responsible for differences in constant terms and in regression coefficients for equations developed on data from different replications of a sample. Multiple correlation coefficients for fat ranged from 0.91 to 0.94 in emulsified meat and from 0.83 to 0.85 in ground meat; for moisture, 0.90-0.94 and 0.83-0.85, respectively; and for protein, 0.80-0.85 and 0.72-0.77, respectively. Overall, near-infrared reflectance shows promise as a rapid method for determining composition of meat. Nevertheless, some aspects of near-infrared reflectance require further attention.

The amino acid sequence of the bovine seminal protein, caltrin, which inhibits calcium transport into spermatozoa, has been determined. The protein contains 47 amino acid residues. Parts of the sequence are identical with that reported for bovine seminal plasmin, a protein possessing antibacterial activity. We believe the proteins are identical and that the previously reported sequence of seminal plasmin is in error.The spermatozoa of mammals are not capable of fertilizing eggs at the time of mating but rather gain this ability after spending some time in the female reproductive tract (1, 2). The biochemical and physiological processes responsible for the acquisition offertilizing ability are termed "capacitation" (3).Two aspects of capacitation have been partially defined. Rabbit spermatozoa that have been incubated 3-4 hr in a capacitation medium (4) or in the uterus (5, 6) acquire a highly vigorous motility characterized by wide excursions of the tail, described as a whiplash movement. The more vigorous motility is accompanied by an increased rate of oxygen consumption (5,6). Earlier we had found that the addition of phosphodiesterase inhibitors or of cyclic nucleoside monophosphate diesters to spermatozoa induces motility and respiration changes similar to those occurring in utero (7,8). It seems quite likely that natural capacitation involves activation of the cyclic nucleotide monophosphate-dependent protein kinases (9) in sperm.The second aspect that has been investigated biochemically is the acrosome reaction (10-12). The acrosome is a membrane-bound compartment covering the anterior portion of the sperm head and containing a variety of hydrolytic enzymes and proenzymes (13). During capacitation, the outer acrosomal membrane fuses with the covering plasma membrane, and the membranes vesiculate and are discomposed, releasing the hydrolytic enzymes.The acrosome reaction can be brought about in vitro by prolonged incubation of spermatozoa in a suitable medium, of which an essential component is Ca2+ (14). It can be induced rapidly by adding the calcium-transporting antibiotic A23187 (15) to spermatozoa in the presence of calcium salts (16,17 (20). Evidence that it is responsible for delaying the acrosome reaction until the sperm are in the vicinity of the eggs has been discussed (20).The present paper describes the sequence of the protein and demonstrates that its molecular weight is 5411. MATERIALS AND METHODSPurification of Caltrin. Bovine semen was the generous gift of American Breeder's Service (DeForest, WI). Caltrin was purified as described (19) except that the final Ultrogel column was replaced with a column (1.7 x 90 cm) of Sephadex G-50 superfine (Pharmacia). Chemical cleavage at tryptophan was done via the procedure of Huang et al. (21). The peptides were separated via reverse-phase HPLC on an Altex C18 column (4.6 x 250 mm) by using a linear 2-hr 0-40% 1-propanol gradient in 0.5 M acetic acid/0.2 M pyridine, pH 4.0.Sequencing. The samples (12 nmol) were sequenced on an Applied Biosystems...