Escherichia coli dihydrodipicolinate synthase: characterization of the imine intermediate and the product of bromopyruvate treatment by electrospray mass spectrometry.

Simplified procedures for assaying and purifying dihydrodipicolinate synthase (EC 4.2.1.52), the first enzyme of the lysine biosynthetic pathway, have been developed and electrospray ionization m.s. has been used to observe the imine intermediate with pyruvate and to investigate the reaction of the enzyme with bromopyruvate and fluoropyruvate.

The basic reproduction ratio for sexually transmitted diseases. Part 2. Effects of variable HIV infectivity.

In this paper we investigate the effects of variable infectivity on the spread of HIV in a heterosexual population where pair formation and separation are taken into account. We calculate the basic reproduction ratio as a function of the number of new partners during the infectious period, keeping the total number of contacts fixed. Numerical evidence suggests that the basic reproduction ratio decreases for variable infectivity if the average infectivity is kept constant.

Integral equation models for endemic infectious diseases.

Endemic infectious diseases for which infection confers permanent immunity are described by a system of nonlinear Volterra integral equations of convolution type. These constant-parameter models include vital dynamics (birth and deaths), immunization and distributed infectious period. The models are shown to be well posed, the threshold criteria are determined and the asymptotic behavior is analysed. It is concluded that distributed delays do not change the thresholds and the asymptotic behaviors of the models.