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Display Omitted Petri net based model of hemojuvelin-hepcidin axis has been proposed.Analysis of the model properties, especially its T-invariants, has been done.Finding dependencies among biological subprocesses corresponding to T-invariants.In non-hepatic cells m-HJV cleavage can be catalyzed simultaneously by two enzymes. Systems biology approach to investigate biological phenomena seems to be very promising because it is capable to capture one of the fundamental properties of living organisms, i.e. their inherent complexity. It allows for analysis biological entities as complex systems of interacting objects. The first and necessary step of such an analysis is building a precise model of the studied biological system. This model is expressed in the language of some branch of mathematics, as for example, differential equations. During the last two decades the theory of Petri nets has appeared to be very well suited for building models of biological systems. The structure of these nets reflects the structure of interacting biological molecules and processes. Moreover, on one hand, Petri nets have intuitive graphical representation being very helpful in understanding the structure of the system and on the other hand, there is a lot of mathematical methods and software tools supporting an analysis of the properties of the nets. In this paper a Petri net based model of the hemojuvelin-hepcidin axis involved in the maintenance of the human body iron homeostasis is presented. The analysis based mainly on T-invariants of the model properties has been made and some biological conclusions have been drawn.

The body iron homeostasis is one of the most important processes in the human body. This complex process is not fully understood and until recently only some parts of it have been described in the literature. In our recent papers the main part of the process has been described and a model based on Petri net theory has been proposed. However, in this model any time dependencies occurring in the biochemical process have not been taken into account. In the present paper the model is enriched in the way that durations of biochemical reactions composing this process have been included into the model. A variant of Petri net where with each place a time interval is associated has been used in order to describe these dependencies. The time interval associated with a place corresponds to a time lag of biochemical conditions which must be fulfilled in order to enable a biochemical reaction to start.

The body iron homeostasis is a not fully understood complex process. Despite the fact that some components of this process have been described in the literature, the complete model of the whole process has not been proposed. In this paper a Petri net based model of the body iron homeostasis is presented. Recently, Petri nets have been used for describing and analyzing various biological processes since they allow modeling the system under consideration very precisely. The main result presented in the paper is twofold, i.e., an informal description of the main part of the whole iron homeostasis process is described, and then it is also formulated in the formal language of Petri net theory. This model allows for a possible simulation of the process, since Petri net theory provides a lot of established analysis techniques.