Abstract: Chemical relaxation studies on the system horse liver alcohol dehydrogenase, nicotinamide adenine dinucleotide, and ethanol were conducted observing fluorescence changes between 400 and 500 nm. Temperature-jump experiments were performed at pH 6.5, 7.0, 8.0, and 9.0; concentration-jump experiments at pH 9.0. The reciprocal of the slowest relaxation time was found to be linearly dependent upon the enzyme concentration for relatively low enzyme concentrations, as predicted earlier. Use of the wide pH-range necessitated expression of the four apparent dissociation constants of the catalytic reaction cycle in terms of pH-independent constants. The system was described in terms of only one (or two) catalysis-linked protons not associated with the electron transfer. Protonic steps in a buffered system are in rapid equilibrium, too fast to be measured with the equipment available. Assuming only two of the four bimolecular reaction steps in the four-step cycle are fast compared to the remaining two, six cases may be considered with six expressions for the reciprocal of the slowest relaxation time. Comparison with the experimental data revealed that the bimolecular reaction steps governing the slowest relaxation time change with pH. Above the effective time resolution of the temperature-lump instrument with fluorescence detection (0.1 msec) only one other relaxation time was detectable and only at pH 9. This relaxation time, found to be independent of the concentration of all reactants within experimental error (r = 10 +/- 5 msec), is most likely due to an interconversion among ternary complexes.

Abstract: Observations of sociosexual behavior of adult ponies, made on two harem groups (each comprised of one vasectomized male and three females), were correlated with follicular development and ovulation for a total of 15 cycles (minimum of 2 cycles per female). Mean cycle length (interovulatory interval) was found to be 19.7 days, with behavioral estrus lasting 7-8 days (5.5 days preovulatory; 2.3 days postovulatory). Estrous females typically showed increased frequencies of approaching and following the stallion, urinating, presenting, clitoral winking, and tail raising. Approaching and following the stallion appeared earlier and persisted longer than other estrous responses. Deviations from the modal estrous pattern included cycles with subestrus, continual estrus, behavioral estrus in the absence of ovulation, and displays of female mounting. Dominance tests revealed that a mare's status was unaffected by the phases of the estrous cycle. The presence of more than one estrous female affected the copulatory performance of both stallions, most notably in reduced latencies to first mount, intromission, and ejaculation, in spite of differences between the stallions in sexual vigor. Each stallion usually selected the dominant mare for copulation when there were multiple estrous females present, but mounts were not displayed exclusively to one female per test. The social testing situation made apparent the importance of use of space in sociosexual communication in this species, particularly in avoidance of the stallion by diestrous mares and standing alone or in proximity to him by estrous mares.