A series of mercaptoacetic acid thiol esters have been identified as metallo-beta-lactamase inhibitors. Electrospray mass spectrometry (ESMS) has shown that irreversible inhibition of the Bacillus cereus II metallo-beta-lactamase by SB214751, SB214752, and SB213079 was concomitant with a 90-Da increase in mass of the enzyme. Tryptic digestion of the B. cereus II inhibited with SB214751 illustrated that the peptide fragment, containing the only cysteine of the enzyme, had undergone a mass increment of 90 Da. It was further demonstrated that B. cereus II hydrolyzed this type of compound across the thiol ester bond to yield mercaptoacetic acid. Mercaptoacetic acid is the only molecular fragment common to SB214751, SB214752, and SB213079, and free mercaptoacetic acid does not bind covalently to B. cereus II. Therefore, it is concluded that these compounds inhibit B. cereus II by the mechanism-based delivery of mercaptoacetic acid, forming a disulfide linkage with the active sites cysteine (predicted mass shift = +90 Da) under the aerobic conditions of the assay. The different thiol esters examined had a broad range of potencies against the metallo-beta-lactamases tested. For example SB214751, SB214752, and SB213079 all had 50% inhibitory concentrations of < 10 and > 1,000 microM for the Stenotrophomonas maltophilia L-1 and Bacteroides fragilis CfiA enzymes, respectively. SB216968 was particularly active against the Aeromonas hydrophila CphA metallo-beta-lactamase and was found to be an uncompetitive inhibitor of this enzyme (Ki = 3.9 microM), whereas it exhibited irreversible inhibition of the L-1 enzyme. These observations with this series of compounds have revealed subtle differences between the active sites of different metallo-beta-lactamases. Finally, a novel application for isothermal titration calorimetry for assessing the zinc chelating activity of candidate inhibitors is also presented.

The structure and function of the stomachs of nine bivalves are examined. These animals belong to the Gastrotetartika, Gastrotriteia, and Gastropempta, the three orders of the Polysyringia, a new sub‐class of the Bivalvia suggested by Purchon (1960a). It is found that in all three orders there are common ciliary tracts and grooves. For example, tracts are always found in association with the duct openings, and a distinction between the right duct tract and the posterior sorting area is drawn. Another tract which is a constant feature of these stomachs, but which has not been noted before, is the antero‐dorsal tract. A generalized polysyringian stomach is constructed. All the stomachs examined function similarly, there being set up in the lumina circulating currents of the gastric fluid. In general, large particles and masses of particles are recirculated until they are broken down, and small heavy particles are rejected by the sorting areas, of which three main types are described. Light particles in suspension in the stomach fluid are carried by the circulating current to the vicinity of the opening of the ducts of the digestive diverticula. The form of the primitive polysyringian stomach and the evolution of sorting areas are postulated. Possible steps in the evolution of the gastropemptan stomach through the gastrotetartikan form are suggested. The function of the appendix is that of a temporary store for large, heavy particles which escape the pallial sortingjnechanisms. It is noted that this organ occurs in all three orders of the Polysyringia.

The septibranch bivalves Cuspidaria rostrata and Cuspidaria obesa are carnivores. The foodcapturing organ is the inhalant siphon, which can be suddenly protruded towards potential prey such as copepods and ostracods, while simultaneously a strong inhalant current is created. When the septum is rapidly contracted blood is forced from mantle sinuses into the rostral and siphonal sinuses, causing the protrusion of the inhalant siphon. The septal contraction also leaves negative pressure in the infra-septal pallial chamber and produces the inhalant current. The stimulus for the directional food-capturing response is a low-frequently vibration which acts upon mechanoreceptors situated in the siphonal tentacles. Small crustaceans are the most frequent prey. Protein digestion is initiated extracellularly in the stomach.

A new species of Solemya is found to lack a gut. It has no provision for the collection of food particles. The ciliation of the mantle cavity functions only to cleanse and irrigate the mantle cavity. Assay of glandular tissues and histochemistry reveal no digestive enzymological apparatus. It is inferred that this species obtains nutriment in the form of dissolved organic molecules. The ctenidia provide a large surface area for such a function, and the lamellae are well supplied with blood. This benthic species, which is most common in the vicinity of pulp mills, lives in a U-shaped burrow in soft mud. The burrow is lined with mucus which is secreted by the large pedal gland. The organism is capable of sustained swimming by repeated adduction of the valves, which causes jets of water to issue from the posterior exhalant opening.

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