No abstract

Upon preincubation with halogenated isoxazolyl-penicillins, the activity of Bacillus cereus 0-lactamase is decreased by a factor proportional to the inhibitor concentration. This inactivation, which concerns essentially the catalytic rate constant of the enzyme, occurs only at or above 37 "C with cloxacillin and dicloxacillin, and even at 25 "C with flucloxacillin. The dependence of the inactivation rate upon inhibitor concentration is consistent, in the former case, with the occurrence of a bimolecular reaction, and in the latter case, with a bimolecular process followed by a monomolecular step.

Lactate-dehydrogenase (LDH) and malate-dehydrogenase (MDH) activities and isozyme patterns of maturing Sertoli cells were investigated in cultured cells obtained from 2-5-week-old rats. Both enzymes, and more strikingly LDH, increased between 2 and 3 weeks of age. LDH isozyme complement included all five isozymes and, in the more mature rats, had a shift toward the isoforms rich in subunit. These data are consistent with an increasing production of lactate/pyruvate and with a finer regulation of this production occurring during the maturing of Sertoli cells. Since lactate/pyruvate are important energy substrates for germ cells, the changes of LDH activity and isozyme patterns of maturing Sertoli cells support their nutritional role in the seminiferous epithelium.

A sensitive and rapid routine method was developed which allows a general, unambiguous and reliable differentiation between fresh and frozen-thawed fish muscle. The suggested procedure consists of (i) mild extraction of muscle in isotonic and buffered medium, (ii) rapid separation of the marker isozymes-those of the mitochondrial aspartate aminotransferase-by cellulose acetate electrophoresis, (iii) specific staining at neutral pH for enzyme activity by sandwich with an agarose-substrate-chromogen pad, and (iv) a clearing and drying process to make a permanent record.

In the foetal human ovary, diameters of oocyte and follicle, as well as those of oocyte and nucleus, are found to be positively and linearly correlated with each other. Follicle diameter and number of granulosa cells also show a positive and linear relationship. Finally, in all ovaries examined, from 5 months after conception onwards, small antral follicles were assessed.