Faecal shedding of canine parvovirus after modified-live vaccination in healthy adult dogs.

Since little is known about the persistence and faecal shedding of canine parvovirus (CPV) in dogs after modified-live vaccination, diagnostic tests for CPV can be difficult to interpret in the post-vaccination period. The primary aim of this study was to determine the incidence, duration and extent of CPV vaccine virus shedding in adult dogs and to investigate related factors, including the presence of protective antibodies, increase in anti-CPV antibody titres and development of any gastrointestinal side-effects. A secondary objective was to assess prevalence of CPV field virus shedding in clinically healthy dogs due to subclinical infections. One hundred adult, healthy privately owned dogs were vaccinated with a commercial CPV-2 modified-live vaccine (MLV). Faeces were tested for the presence of CPV DNA on days 0 (prior to vaccination), 3, 7, 14, 21 and 28 by quantitative real-time PCR. Pre- and post-vaccination serum titres were determined by haemagglutination inhibition on days 0, 7 and 28. Transient excretion of CPV DNA was detected in 2.0% of dogs before vaccination. About one quarter of dogs (23.0%) shed CPV DNA during the post-vaccination period, but field and vaccine virus differentiation by VP2 gene sequencing was only successful in few samples. Faecal CPV excretion occurred despite protective serum antibody titres. Post-vaccination CPV shedding was not related to adequate antibody response after vaccination or to the occurrence of gastrointestinal side-effects. Despite individual differences, CPV DNA was detectable for up to 28 days after vaccination, although the faecal CPV DNA load in these clinically healthy dogs was very low.

On the Participation of Phosphoribulokinase in the Light Regulation of CO(2) Fixation.

CO(2) fixation by a suspension of isolated spinach chloroplasts was terminated by turning off the light, and changes of metabolite levels in the chloroplast stroma and the surrounding medium were assayed. Whereas CO(2) fixation comes to a total stop within 15 seconds, a conversion of triose phosphates to heptose, hexose, and pentose monophosphates is found to occur for 1 to 2 minutes afterwards. It seems from these data that an inactivation of fructose and sedoheptulose bisphosphatases proceeds with a lag period. In contrast, the conversion of pentose monophosphates to ribulose 1,5-bisphosphate is inhibited immediately after the stop of illumination. As the stromal level of freely available ATP was not depleted under this condition, these data demonstrate that ribulose 5-phosphate kinase was very rapidly inactivated after darkening of the chloroplasts. Essentially, the same effect is also observed when CO(2) fixation is partially inhibited by addition of moderate concentrations of m-chlorocarbonyl phenylhydrazone, partially uncoupling photophosphorylation. It appears from these results, that the activity of ribulose 5-phosphate kinase is not only regulated by light through the mediation of reduced carriers like thioredoxin but also by alternative parameters, e.g. stromal metabolite levels.

Balance between Metabolite Accumulation and Transport in Relation to Photosynthesis by Isolated Spinach Chloroplasts.

The relationship between the rate of orthophosphate (Pi) transport into the stroma and the rate of CO(2) fixation by intact chloroplasts was investigated. High Pi concentrations in the medium lead to a depletion of stromal metabolites, due to excessive Pi transport into the stroma, resulting in the inhibition of CO(2) fixation. This inhibitory effect of Pi is released by inhibitors of Pi transport, such as pyrophosphate, citrate or pyridoxal-5-phosphate. The latter compound appeared to be specially valuable in inhibiting Pi transport without affecting stromal reactions.The Pi optima of CO(2) fixation were studied when the rate of CO(2) fixation or the rate of Pi transport was varied by the application of specific inhibitors. For optimal performance the rates of CO(2) fixation and Pi transport have to be matched in such a way, that transport neither limits nor exceeds CO(2) fixation. This accounts for the large variation in the Pi optima for CO(2) fixation by different chloroplast preparations.

The mechanism of the control of carbon fixation by the pH in the chloroplast stroma : Studies with acid mediated proton transfer across the envelope.

The salts of several weak acids have been used to render the envelope permeable to protons. In order to investigate the role of stromal pH changes in the light regulation of CO2 fixation, formate, octanoate, nitrite, and glyoxylate have been tried as tools to reverse the light-dependent alkalization of the stroma. For this purpose, the decrease of the stromal pH in illuminated spinach chloroplasts, as caused by the addition of these substances or by instantaneous lowering of the pH in the medium, has been compared with the corresponding decrease of CO2 fixation and the change of stromal metabolite levels. It appears from out data that formate and octanoate are suited best to obtain a specific inhibition of CO2 fixation by lowering the stromal pH. The measurement of the corresponding metabolite levels indicates that this inhibition is primarily due to an inhibition of fructose- and sedoheptulose bisphosphatase. It is concluded that these two enzymes are important regulatory steps for the light control of CO2 fixation.