delta 4-5 alpha-Reductase activity is apparently regulated by a testicular factor(s) secreted directly into the epididymis, whereas 3 alpha-hydroxysteroid dehydrogenase activity, in this tissue, appears to reflect circulating androgen levels. To test whether the factor(s) regulating delta 4-5 alpha-reductase activity is directly associated with spermatozoa, a developmental study was undertaken to temporally correlate various parameters of the male reproductive tract with enzymatic activities. delta 4-5 alpha-Reductase activity is first detectable at 21 days of age. Activity increases until day 77, after which time enzymatic activity decreases by more than 60%, reaching steady adult values at 105 days. 3 alpha-Hydroxysteroid dehydrogenase activity is detectable as early as 7 days. Levels of this enzyme increase until day 63, after which time constant adult values are maintained until at least 1 yr. Spermatids and/or spermatozoa are first seen in the testes at 42 days, and plateau levels are reached by day 77. Spermatozoa are first seen in the epididymis at 49 days and reach maximal values by 91 days; no significant change occurs thereafter (until 365 days). Increases in seminal vesicle and ventral prostate weights are of a sigmoidal type, paralleling increases in plasma androgens, with the greatest rate of rise between days 35--63. This sigmoidal type of increase in tissue weights and plasma androgens is similar to that seen for epididymal 3 alpha-hydroxysteroid dehydrogenase but markedly different from that found for delta 4-5 alpha-reductase. The importance of delta 4-5 alpha-reductase and 3 alpha-hydroxysteroid dehydrogenase activities in the epididymis before the entry of spermatozoa and the decline in delta 4-5 alpha-reductase activity with age is discussed.

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alpha‐Latrotoxin (alpha‐LTx, apparent mol. wt. 130 000) is a presynaptically active neurotoxin purified from the venom of the black widow spider that causes massive exocytotic release of neurotransmitters, presumably via binding to presynaptic membrane protein(s). Solubilization and purification experiments were undertaken to identify and characterize this membrane component. An immunoaffinity matrix was prepared by sequentially binding anti‐alpha‐LTx antibodies and alpha‐LTx to Protein A‐Sepharose CL‐4B. Beads were irreversibly cross‐linked with dimethyl pimelimidate. These beads were capable of extracting alpha‐LTx binding activity from Triton X‐100 solubilized bovine synaptosomal membranes. Following extensive washing, bound material was eluted with 6 M urea. Analysis of silver stained and radiolabel‐containing gels revealed one major band (apparent mol. wt. 200 000) under non‐reducing conditions and two major bands (apparent mol. wts. 66 000 and 54 000) under reducing conditions. The purified material was still capable of specifically binding alpha‐LTx as determined by solid phase assays on microtiter plates. The affinity for alpha‐LTx of the purified preparation was similar to that of the native membrane (KA approximately 10(10) M). It is concluded that a putative alpha‐LTx receptor protein can be purified from synaptosomal membranes using an immunoaffinity matrix in a form that retains its defined biological property (alpha‐LTx binding).

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