def statement_present_verb(stmt_type):
    """Return the present verb form of a statement type.

    Parameters
    ----------
    stmt_type : str
        The lower case string form of a statement type, for instance,
        'phosphorylation'.

    Returns
    -------
    str
        The present verb form of a statement type, for instance,
        'phosphorylates'.
    """
    override = {
        'complex': 'binds',
        'regulateamount': 'regulates the amount of',
        'increaseamount': 'increases the amount of',
        'decreaseamount': 'decreases the amount of',
        'gef': 'acts as a GEF for',
        'gap': 'acts as a GAP for',
        'inhibition': 'inhibits',
        'gtpactivation': 'activates when bound to GTP',
        'regulateactivity': 'regulates the activity of',
        'activeform': 'has active form',
        'conversion': 'converts',
        'influence': 'influences',
        'modification': 'modifies',
        'addmodification': 'adds a modification to',
        'removemodification': 'removes a modification of',
        'selfmodification': 'modifies itself',
        'event': 'happens'
    }
    return override.get(stmt_type) if stmt_type in override else \
        stmt_type[:-3] + 'es'