A study of the single polypeptide nature of rhodanese. A comparison of different preparations

The enzyme rhodanese (EC 2.8.1.1) appears as a single polypeptide chain protein on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The molecular weight of this species is approx. 33 000. This contrasts with previous reports that rhodanese behaves on gel filtration chromatography as a rapidly equilibrating monomer-dimer system composed of identical subunits with a molecular weight of 18 500. We have investigated this apparent discrepancy by isolating the enzyme by the two different preparative procedures used in the above investigations. The two crystalline samples were subjected to gel filtration chromatography under a wide variety of conditions and to sodium dodecyl sulfate disc gel electrophoresis. The two preparations yielded rhodanese which behaved identically and no evidence for the monomeric species was obtained under any experimental condition tested. Thin-layer gel chromatography of clarified liver homogenates gave no evidence of rhodanese species other than that present in the purified samples. The variation in molecular weights observed in gel filtration chromatography may be a reflection of the conformational mobility of the enzyme leading to solvent-dependent changes in Stokes radius. If rhodanese is dimeric, special interactions must stabilize it under the conditions tested here.

Minor salivary glands as a major source of secretory immunoglobin A in the human oral cavity

Secretory immunoglobulin A is the predominant immunoglobulin in labial minor salivary gland secretions. Its mean concentration is four times higher in these secretions than in parotid gland secretion. The minor salivary glands can produce 30 to 35 percent of the immunoglobulin A that enters the oral cavity. This, together with the potential accessibility of these glands to antigenic stimulation, suggest that they may be an important source of the immune factors that are involved in the regulation of the microorganisms in the oral environment.

Pharmacological studies on feline Betz cells

1. A study has been made of the sensitivity of single neurones in the pericruciate cortex of anaesthetized and unanaesthetized cats to cholinomimetics administered electrophoretically from multibarrel micropipettes.2. A high proportion of deep pyramidal cells, including Betz cells, were excited by these substances, and the receptors involved have muscarinic characteristics.3. Atropine specifically reduced the sensitivity of cortical neurones to acetylcholine, but no such action could be demonstrated for dihydro-beta-erythroidine, gallamine or general anaesthetics.4. The significance of these results is discussed in relation to the possible synaptic or non-synaptic action of acetylcholine upon cortical neurones.

Acetylcholine sensitivity of cerebellar neurones in the cat

1. Cholinomimetics, acetylcholine antagonists and some other compounds of pharmacological interest were administered electrophoretically near neurones within the vermal cerebellar cortex of anaesthetized (pentobarbitone) and unanaesthetized (cerveau isolé) cats.2. The neurones were identified by position within the cortex, spontaneous activity, and the responses to afferent and antidromic stimulation.3. Purkinje cells, but neither granule nor basket cells, were excited by cholinomimetics, and the acetylcholine receptors had muscarinic properties. Excitation was often preceded by depression of the spontaneous firing.4. Intravenously administered atropine and dihydro-beta-erythroidine did not depress the synaptic excitation of cerebellar neurones evoked by impulses in mossy, climbing or parallel fibres.5. Acetylcholine is thus unlikely to be an excitatory transmitter within the feline cerebellum, particularly at mossy fibre-granule cell synapses, despite the presence of relatively high levels of acetylcholinesterase within mossy fibre terminals.