The thioredoxin-like fold is a well conserved fold that is present in many families of proteins. One such superfamily of proteins include the GSTs which are involved in phase II detoxification. GSTs primarily catalyse the metabolism of xenobiotics but are also involved in transporting non–substrate ligands and reactive compounds. The GST fold comprises an N-terminal thioredoxin domain and an all alpha helical C-terminal domain and is present in at least 18 classes of proteins. The N-terminal thioredoxin domain is characterised by the βαβαββα topology and can be further divided into two structural motifs, an N-terminal (βαβ) and a C-terminal (αββα) motif. A well conserved hydrophobic network exists between these two motifs and the role of the C-terminal motif is elucidated in this study using class Alpha GST as a model protein. A topologically conserved valine (Val58) and an isoleucine (Ile75) located on β3 and α3, respectively, were mutated to alanine. Secondary and tertiary structural characterisation as well as ligandin function of the mutant enzymes displayed no major structural alteration with respect to the wild-type enzyme. This was confirmed with high resolution crystal structures obtained. Enzymatic activity was maintained indicating that no structural alterations have occured that affects the active site dynamics and the domain interface as a result of the induced mutations. Thermal denaturation studies, however, indicated a slight destabilisation in the enzyme in the case of the valine mutation, but a large destabilisation was witnessed as a result of the isoleucine mutation. This is further observed in denaturant-induced equilibrium studies where the thermodynamic stability of proteins can be determined. Furthermore, as a result of the isoleucine mutation, the enzyme unfolds via a populated intermediate in contrast to the wild-type which globally unfolds via a two-state mechanism with no stable intermediates being populated. Pulse-proteolysis was employed as an additional probe for thermodynamic stability where the enzyme was digested by thermolysin at varying denaturant concentrations. Pulse-proteolysis results were in agreement with the thermal and denaturant-induced stability studies further confirming that the isoleucince substitution causes a large destabilisation. Thus these conserved hydrophobic residues of the thioredoxin C-subdomain play a crucial stabilising role in the GST fold.

Thesis (M.Com.(Taxation))--University of Pretoria, 2009. / Abstract in English and Afrikaans. Includes bibliographical references.

Thesis (doctoral)--Universität Berlin.

No description available.

M.Com. (Economics) / The objective of the thesis is to examine the fiscal importance' of indirect taxation with specific reference to value added taxation. The investigation takes cognisance of the unique characteristics of the South African economy, especially its strong dualistic characteristics, very unequal distributlon of income and extensive backlogs in the areas of social services and infrastructure. The South African tax system has undergone a rather fundamental shift in the early 1970s when the sales duty was replaced by a general sales tax. This tax, implemented in July 1978 at the rate of 4 per cent provided for the exemption of basic foodstuffs and the issuing of exemption certificates mandating the non-taxation of certain goods. These certificates led to abuse and fraud. The tax was a cascading tax and double taxation was an inherent characteristic of it. Within 13 years of its existence the rate of the tax soured to 13 per cent. An European-styled value added tax, engineered on the New Zealand model, was implemented in September 1991. Value added tax has in the past been criticised on account of its regressive properties. Unions have depicted value added tax as an unfair tax because of its skewed income and wealth effects. Providing relief for the perceived regressivity of valued added tax is not an easy decision. The regressivity of value added tax can be reduced by zero ratings, differential rates and exemptions, but it was found that there are convincing reasons why the value added tax base should be kept as broad as possible. Internationally it is accepted that economic distortions are kept to a minimum when value added tax is levied on a broad base with a minimum number of zero ratings and differential rates. A broadly based tax effects current and future consumption to the same degree and is therefore neutral as to consumption and saving. Irrespective of this best-policy-advice, various countries still make considerable use of zero ratings and differential rates to lessen the regressivity of the tax system. Theoretically value added tax does not add to inflationary pressures. Notwithstanding this theoretical view there is some evidence that value added tax could sometimes lead to cost push inflation should compensating salary increases follow after a broadening of the base. The dissertation agrees with South African studies indicating that the cascading effects of value added tax is negligible. Although the rate of inflation increased during the twelve month period following the introduction of the tax in South Africa, it had an once-off impact on the general level of prices and could thus not be typified as inflation. Financial services are by and large exempted from value added tax due to its many definitional problems. In this connection, the Poddar-English model is regarded by some observers as a means of addressing this problem. The model does not provide solutions for all the problems and remains to a large extent impractical. Notwithstanding this, the extension of the tax base to include financial services will enhance the efficiency of the tax.

Assignment (MRek)--University of Stellenbosch, 2006. / Bibliography. Also available via the Internet.

Thesis (D. Comm.)--University of Pretoria, 2003. / Includes bibliographical references (leaves 160-168).

M.Comm. / The objective of this dissertation is to examine the desirability of implementing place of supply rules as an instrument to reduce uncertainty in the South African value-added tax system, specifically with respect to cross border transactions. Value-added tax systems have been introduced in many countries, and experienced a marked increase in popularity, especially since the 1970's. Value-added tax systems often replaced sales taxes due to the many benefits a purist value-added tax system has to offer. The opening up of the world economy brings the importance of cross border transactions to the fore. Many countries recognised the fiscal uncertainty and imbalances an ever-increasing number of cross border transactions can bring to a country's value-added tax system. Place of supply rules were introduced into the value-added tax systems of many of these countries to enhance legislative certainty, to avoid double taxation and to increase equity of the overall tax system. However, when South Africa introduced value-added tax in 1991, South Africa was to a large extent still isolated from the world economy. Since the earlier 1990's, particularly since 1994 when South Africa instated its first democratically elected government, the world economy started opening up to South Africa. South Africa's value-added tax system did not and still does not have certainty on place of supply rules. Though, technically, South Africa's value-added tax system seeks to tax most, if not all, transactions with a South African connection, vendors in South Africa, tax consultants and the South African Revenue Service are experiencing difficulty (to some varying degree) on interpreting the value-added tax consequences of cross border transactions. Place of supply rules have been mooted by various role-players, the South African Revenue Service and value-added tax practitioners alike, as a possible solution to the current uncertainty in respect of cross border transactions. The relevance and desirability of introducing place of supply rules in South Africa need to be assessed.

There has been a growing interest in recent years in the Value Added Tax (hereinafter referred to as the VAT). Interest in tax reform is perennial but the factor which has generated such wide interest in the VAT has been its adoption by the member countries of the European Economic Community (EEC). The recent entry of Britain into the EEC and her adoption of the VAT have increased South African interest 1n the system because of the strong trading ties between our two countries. The Franzsen commission on taxation in South Africa gave some attention to VAT but in their own opinion not enough. This is clear from their statement: "The Commission is aware of the fact that a transition from the selective sales tax which rests on a commodity basis to a Value Added Tax, which is essentially a turnover tax, implies important administrative changes. It is felt, nevertheless, that the Value Added Tax merits further study". This thesis hopes to satisfy some of that need for further study. The aim of the thesis is not to arrive at a definite conclusion as to whether South Africa should or should not adopt the VAT, indeed, it may be impossible to answer this question completely objectively. Rather the thesis sets out to examine the implications, both theoretical and practical, of a VAT, and to present certain guide-lines as to what may constitute the best form of a VAT should it be decided to introduce this mode of taxation. There is no separate section on South Africa. Instead, the implications for South Africa have been integrated into the main body of the text. For this reason, the emphasis throughout has been on the VAT replacing the selective sales tax and, to a lesser extent, the profits tax. It is felt that the selective sales tax would be the tax most likely to be replaced by the VAT in South Africa, and that the added revenue which could be collected from the broader-based VAT could possibly be off-set against the revenue lost on a reduction in company profits tax. Such a measure would certainly be well received among business men.

M.Comm. / VAT is a tax that is based on taxing the value added on successive transactions in the supply chain, accordingly it is a tax designed for the retail or manufacturing industries. South Africa introduced VAT that is similar to that introduced across the world and later refined it. The revisions included the introduction of VAT on banking services. The introduction of VAT to banking is a first in the VAT world but still does not find a cure for the principle dilemma of taxing a bank's value added, under VAT. The study therefore established if banks are treated fairly by investigating: • The three canons of taxation, • The eight principles on which VAT rests, • And the agreement between SARS and the Council of South African Banks. The reason of the above is to propose enhancements or an alternative design that would either increase the accuracy, equity, or simplify the calculation of VAT in the banking sector. The study found that there are several options when introducing VAT to the financial services sector, namely: • zero rate it and the fiscuss looses out on the output VAT, • tax it and increase the cost of borrowing as well as face the problems of determining the value added per transaction or; • exempt it and a practice known as cascading takes place. Neither of these solutions seemed viable although the full taxation option is conceptually the only correct method oftaxation. In most countries the exemption option was taken. The result of exempting interest is that banks have to apportion their input VAT. There are various options open to a bank when calculating the ratio of input VAT to be claimed, yet legislation has only made mention of two. To alleviate this situation the VAT authorities and the Council of South African Banks have agreed upon a methodology to calculate the ratio of input VAT to be reclaimed. This agreement is not compulsory and only applies to areas where the bank does not have an alternative apportionment technique, and in some instances is also flawed in its logic. Consequently banks have the option to apportion input VAT on what they perceive to be a fair basis. The indecision and inequities described above does not result an accurate VAT. The conclusion was that the design is urtiust and the practical calculation, when applied, does not the deliver the correct amount of tax payable. The study introduced a different form of VAT, named the Business Transfer Tax. This tax is an additive form of VAT, based on accounts that relate to interest and trading income. Interest income and trading income would be zero rated under the current VAT, and therefore entitle the bank to claim input tax incurred on expenditure. This would overcome all of the issues not resolved previously.